Bad Astronomy
The entire universe in blog form

June 24 2016 9:00 AM

Neptune Just Got a Little Dark

So Thursday I wrote about Pluto possibly having a liquid water ocean under its surface, which is pretty amazing. But other worlds in the solar system have stuff going on too, y’know.

Like Neptune. It has a new dark spot.

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Neptune is what we call an ice giant; bigger than rocky planets like Earth and Mars, but smaller than Jupiter and Saturn. It’s not literally made of frozen stuff; it’s called an ice giant because planetary scientists tend to call things like methane, ammonia, and water ices when dealing with outer worlds.

Neptune orbits pretty far from the Sun, about 4.5 billion kilometers out. That makes it pretty cold, and you might not expect the atmosphere to have much action. For a long time telescopic observations of it didn’t show much (it’s so far away that even though it’s nearly four times wider than Earth, it’s not terribly big in telescopes), but in 1989 the Voyager 2 probe flew past it, revealing a gorgeous deep blue world with a banded atmosphere, and, very surprisingly, a huge dark spot, which was somehow named the Great Dark Spot.

Since then our ‘scopes have gotten better and more of these spots have been found. We now know they’re anticyclones—high pressure systems—in Neptune’s troposphere, the deeper layer of atmosphere under its stratosphere. Since they’re high-pressure systems, we may be peering deeper into Neptune’s atmosphere when we see them.

color view of Neptune
When full color filters are used, the brighter, whiter clouds appear.

NASA, ESA, and M.H. Wong and J. Tollefson (UC Berkeley)

Dark spots on Neptune tend to be associated with bright clouds around their rims, which may be from methane clouds condensing as air blows around and above the dark spots. This happens on Earth …  well, with water instead of methane. Moist air rising up can condense to form clouds; we see this on the windward sides of mountains as the air lifts up to go over the obstacle. In this case, they’re called orographic clouds. With Neptune, the methane freezes, crystallizes, and becomes bright white to form the lovely thin white clouds around the dark spots.

Dark spots come and go. The Great Dark Spot had disappeared by the time Hubble looked for it in 1994, but other ones had appeared in 1995. This new one found is the first one seen in well over a decade. They can last for many years, because they spin in the same direction Neptune does. That sets up a stable feedback system that helps keep the spot rotating (in that case it’s called a vortex). We see this on Jupiter, Saturn, and possibly other places on Neptune, too.

Why is this important? Well, to be frank, atmospheres are complicated. Planets spin, and warm up, and have different stuff in their atmospheres, and sometimes warming or cooling changes the layering and condensation and evaporation rates, and it’s a mess. Understanding them in terms of their physics is really hard.

In some ways the outer planets are simpler than Earth: They’re mostly air. But there are other complications, like gases in abundance we don’t have here (like hydrogen and helium). Also, while the major source of Earth’s heat is the Sun, the outer planets don’t get nearly as much sunlight. Plus, they still have lots of warmth leftover from their formations (yes, they’re still cooling after 4.56 billion years), and for Neptune that’s its major source of heat. So it’s warmed from the inside out, the opposite of Earth.

All these worlds are test cases for our understanding of how atmospheres behave, including our own. Plus, of course, just understanding things is good. Neptune is a huge, massive, complex world, and worthy of our attention just because it exists and is near enough for us to study it.

June 23 2016 9:00 AM

Does Pluto Harbor an Ocean Under All That Ice?

Before the New Horizons space probe zipped past Pluto in July 2015, we weren’t sure what to expect. A lot was known about Pluto in general—given its density, it was likely a mixture of ice and rock, for example—but very little about was known about, say, the surface structure.

Then the little spacecraft flew by the little world, and our knowledge exploded. The close-up pictures were amazing, both beautiful to behold and tantalizing for the brain. There were lots of surprises, of course, including how diverse the surface was: There are frozen plains of nitrogen, mountains of water ice, dark and bright spots, huge fields of pits on the surface, and much more.

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Scattered around the surface are another type of feature: huge cracks, some hundreds of kilometers long and many kilometers deep. They’re pretty interesting, and their presence has led one group of planetary scientists to make an astonishing claim: There may be a liquid water ocean under the surface of Pluto!

If this is true, it’s a very big deal. Pluto is small and extremely cold, so the last thing you’d expect is liquid water anywhere within 3 billion kilometers of it. How can this be?

First, the evidence. The cracks are called extensional tectonic features, meaning you get them when the surface extends, expands. Imagine covering a balloon with mud. Let the mud dry, then inflate the balloon a little bit. What happens? As the balloon expands, it pushes the mud from underneath. Mud isn’t stretchy like rubber, so instead of smoothly expanding it cracks, allowing the pressure underneath to be relieved.

That may be happening on Pluto. The solid crust (mostly water and nitrogen ice) is feeling pressure from underneath, expanding, and cracking. But what could be causing the expansion? Liquid water. And lots of it.

Pluto is mostly ice and rock. However, there is likely to be some amount of radioactive elements in its core. Our own Earth has them, and the heat generated by the decay of these elements is a major source of our planet’s internal heat, even 4.56 billion years after it formed.

Pluto interior
Pluto's layers may include a crust of ice, a liquid ocean under that, and a large core of mostly rock with just enough radioactive material to keep it warm.

Jcpag2012/NASA/Pat Rawlings/Phil Plait

Studies show that even a small amount of such material (including uranium, thorium, and potassium) could produce enough heat inside Pluto to melt some of the water ice. I’ll admit this surprised me; my gut reaction is that Pluto is so small that it would lose heat faster than the radioactive materials could generate it.

The new research just published looks into that. They show that the rocky material inside Pluto insulates it and keeps that heat from leaking away too quickly. The rock acts like a blanket, keeping the heat inside Pluto, and over time it could be enough to not only melt a substantial amount of ice, but keep it liquid even to today.

Well, mostly liquid. Pluto is pretty cold, and some of that water, especially closer to the surface, could start to freeze. When liquid water turns into ice, it expands, and it’s that expansion that’s proposed to cause the crust of Pluto to expand with it, creating the cracks.

How weird is that? Tiny, frigid Pluto, long thought to be a frozen ball of ice, may yet have some spring in its step.

And there’s more. The new research shows that if the ice shell covering Pluto is thick enough—deeper than about 260 km—then the water under the surface could form a strange kind of ice called ice II. It’s still made up of water molecules like regular ice, but under higher pressures (caused by the thicker shell) the molecules realign themselves, forming a different crystal structure than normal ice.

Ice II is denser than regular ice, denser even than liquid water. If it forms, the ocean under the surface would shrink, contracting to a smaller volume. If that happened, you’d expect to see compressional features on the surface of Pluto, like thrust faults.

However, none was found, so it’s unlikely ice II ever formed. That suggests the water under the surface is still liquid, even today. Incidentally, the cracks on Pluto are fresh-looking, with few craters marring them. This indicates relative youth, though it’s hard to know what that means on Pluto. Millions of years? Tens of millions?

Still, this is an intriguing idea. I expect there will be some back-and-forth on this, as the surface of Pluto is examined more closely. For example, there’s a mountain on Pluto that looks like it was pushed up, and then began to subside. If that’s the case, what does that tell us about the thickness of the crust there, and the forces underneath? Also, there are cracks on Pluto’s surface that aren’t linear so much as radial, as if whatever pressure under the surface were greater there than average. Maybe there’s material welling up there, pushing up on the surface.

And of course, there’s another thought. A source of heat, liquid water, and complex chemicals are three ingredients needed for life. Now have a care here: I am in no way saying there’s life under Pluto’s surface! My point is more subtle than that: We wonder if life exists out in the Universe, and the key to that is how commonly the necessary conditions arise. What we’re seeing on Pluto—and on Enceladus, and Europa, and Titan—is that these conditions at least in part appear to pop up quite a bit just in our solar system alone. Even in almost literally the last place you’d expect.

Oh Pluto, will you ever stop surprising us?

I certainly hope not.

June 22 2016 9:00 AM

On the Ball of the Midnight Sun

Imagine you are on a large sphere.

Got it? Now imagine that sphere is spinning. As it does, two poles are defined: You can call them what you like, but “top” and “bottom” work. Halfway around the sphere from the top one toward the bottom is the sphere’s midsection. You can call it what you like, but “waist” works.

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Now imagine there’s a source of light some distance off. Imagine too this source of light is carefully placed such that the axis of rotation of the sphere is perpendicular to the direction to the light. In other words, the sphere spins vertically. The light then illuminates half the sphere, but as the sphere spins every point on its surface will eventually get lit during one rotation.

If you stand on a pole, let’s say the top one, you spin in place, once per sphere rotation. To you, the source of illumination spins around the sky, neither rising nor setting. It just goes around. The same is true if you’re on the bottom pole, too.

If you’re on the waist, in one spin you make a big circle, the size of the circumference of the sphere. For half a spin the source of illumination is visible, but for the other half it’s behind the sphere and you can’t see it. The light rises, goes directly overhead, and sets again after half a rotation, then rises again a half rotation later. If you’re anywhere else on the sphere except a pole (and if the sphere is very large compared to you), the Sun will rise and set but won’t go overhead.

But now let’s tilt the sphere. It can go any way, but let’s say the top pole it tipped toward the light. If you stand on the waist, the light still rises and sets, but instead of going overhead it makes a lower arc in the sky, never quite reaching the overhead point. How much it misses depends on how much the sphere is tilted.

tilted Earth
Maybe you see where I'm going with this.

Phil Plait

If you stand on the bottom pole, tipped away from the light, you’re still spinning in place, but you’re facing away from the light. The light is always blocked by the sphere, so you never see it. It’s always dark.

If you stand on the top pole, you’re still spinning in place, but now the light appears to go up and down over one spin. It doesn’t get blocked by the sphere, but it does get low, close to where the sphere blocks the sky (let’s call that the “horizon”). If you move away from the pole, down toward the waist by just the right amount, then the light will just kiss the horizon as it dips down before moving back up again. The distance you have to be from the pole for it to do this depends on the amount the sphere is tipped.

Now. If you’re on the top pole, what would that look like?

That wonderful time-lapse video was taken by astrophotographer Göran Strand just a little more than a day ago. He was standing on a big sphere—the Earth. The Earth is tilted, by about 24°. It goes around the light source (the Sun), but the tilt stays the same, so at one point in that journey the top (north) pole is tipped as much toward the Sun as it can be. We call that point in its orbit the solstice.

Strand was just the right distance from the North Pole, so that the path the Sun made in one rotation (one day) just barely stays above the point where the Earth blocks the sky (the horizon). He saw it make a big circle in the sky, taking one spin (one day) to go around.

Someone much farther away from the pole saw the Sun rise and set over the course of that day, but not Strand. Whereas it was the middle of the night for that person farther away, Strand never saw the Sun leave the sky.

And that’s why this phenomenon is called “the Midnight Sun.” Strand took that photo from just inside the Arctic Circle (24° south of the north pole), in Gällivare, Sweden, at just about midnight local time. Gällivare is at a latitude of 67°N, or 90 – 67 = 23° from the pole. Anyone there or closer to the pole never saw the Sun set that day.

And anyone inside the Antarctic Circle, 24° away from the south pole, never saw the Sun rise that day. It’s always night there right now, and if you’re on the pole you won’t see the Sun rise until September.*

Think of it! You are on a tilted sphere that is madly spinning as it whirls through space around a distant light source, creating day and night and seasons and climate and weather, which over billions of years has impacted geology and sculpted life to adapt to the day/night cycle, the annual cycle, the change in light versus distance from the poles. We set our calendars to these cycles, our clocks, our very lives to these cycles caused by our rotating, oblique planet.

Don’t think science affects your life? Think again. It affects everything.

* Right now, two members of an NSF team there are very ill, and a rescue mission has been mounted to bring them back north for medical attention. It is always dark there, and very, very cold, so this is nothing short of a heroic effort. The plane landed there on Tuesday and has begun the arduous journey back.

June 21 2016 9:15 AM

Two Baby Alien Worlds Show Us How to Cook a Planet

Two new exoplanets have been discovered, and they’re important milestones in our understanding of how alien solar systems behave. That’s because both are very young, both are massive, and both orbit their stars very close in, closer than Mercury orbits the Sun.

First, a quick intro to the problem: When astronomers first started finding planets around other stars in the mid-1990s, they were surprised to find that many were as big and massive as Jupiter but so close to their parent stars that they had orbital periods measured in days. Given that Mercury, the innermost planet in our solar system, is small and takes three months to circle the Sun, these “hot Jupiters” were pretty shocking. How did they get there?

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Models of planetary formation show that it’s very unlikely a big planet can form so close to the star. Most likely, they form farther out and somehow migrate in toward the star. One way would be to interact with the disc of debris circling the star from which the planet formed. As it plows into this material, it can drop down to the star. It’s unclear if this happens very early in the life of the planet (like, within a million years or so after it forms) or much later, like right before the debris disk is blown away by the star millions of years later.

Another way would be for it to gravitationally interact with other planets in the system, which can affect their orbits. This method takes a while, though, and is slower in general than the debris disk method. The problem: Most planets found are old, a billion years or more, so it’s hard to know just when the hot Jupiter moved.

These two new planets change that.

One is called K2-33b and was found by the Kepler spacecraft, the one that has discovered so many alien worlds. The star, K2-33, is about 460 light-years away and is a cool red dwarf, only about 0.6 times the mass of the Sun and shining at a feeble 15 percent as bright*. It’s part of a loose cluster of stars called the Scorpius-Centaurus OB Association, which is known to be young. The colors of the star also indicate youth (it’s still very hot from its formation, so it’s bluer than you’d expect), and the smoking gun is the presence of lithium in the star’s atmosphere; that element gets destroyed by a star very quickly, so seeing any at all means the star is very young. All together, this points to an age of no more than 20 million years, and most likely closer to 11 million years.

Our own Sun is 4.56 billion years old, so this star is basically a wee bairn.

K2-33b, the planet (note the “b”) is roughly 60,000 kilometers across, a bit less than five times Earth’s diameter. It has no more than the mass of Jupiter, and likely has less—it’s more like a super-Neptune or a mini-Jupiter. It orbits the star every 5.4 days, so it’s close.

Given its youth, that strongly indicates that massive planets can migrate rapidly toward their star right after they’re born, perhaps even while they’re still forming.

K2-33b orbital scale
When I say close, I mean close: K2-33b orbits its star a lot closer even than Mercury does the Sun.

NASA/JPL-Caltech

But wait! There’s more! We have the other planet, too.

Before I even get started, let me say that this second planet has not yet been confirmed, but given the circumstances it seems very likely it’s real. I’d be happier with more independent evidence, but the authors indicate the probability of it actually existing is very high.

This one orbits the star V830 Tau, which has a mass almost the same as the Sun, but is twice the radius and about 20 percent more luminous. The planet orbits the star every five days at a distance of just 8.5 million kilometers—that’s very close indeed. Even better, the age of the star appears to be only about 2 million years, which is even younger than K2-33!

So, in both cases, we have a massive planet, which is orbiting very close to its star and is very young. That’s very exciting! They show that planetary migration can happen almost immediately, even as the planet and star are still settling down after their formation.

Mind you, this doesn’t mean planets don’t move later in life. In fact, we have evidence that planetary interactions do happen (some planets orbit their stars backward, in the opposite sense of the star’s rotation, which can happen if the planet has undergone a game of celestial billiards with other planets).

So what we now seem to find is that there’s more than one way to cook a Jupiter, and it can happen right away or it can take a while.

This is amazing. I’ll remind you that until 1995 we didn’t even know if other planets existed around other stars like the Sun. It’s only been 20 years, and we’ve learned so much about them! We have thousands to study, and they come in so many flavors: Big, small, hot, cold, puffy, compact … we see planets like the ones in our solar system, and ones that are entirely alien.

And we’re still just getting started here. We know of something like 3,000 planets right now, but there are likely hundreds of billions in our galaxy alone! With a sample size that vast, even something very unlikely is bound to happen. What other strange new worlds await us?

* Correction, June 21, 2016: I originally wrote that K2-33 has a diameter of 0.6 times the Sun's, but I meant the mass. Weirdly, it's actually about the same size as the Sun, because it's still so hot from formation that it's inflated a bit. It'll shrink as it ages.

June 20 2016 11:01 AM

Happy Full Moon Solstice!

On Monday at 22:34 UTC (6:34 pm Eastern U.S. time), the Sun will reach its highest declination in the sky, its farthest point north for the year. That is the moment of the June solstice.

This means that, in the Northern hemisphere, we have the longest day of the year, and the shortest night. If you live your life standing on your head in the Southern hemisphere, it means you have the shortest day, and the longest night.

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I enjoy writing about the solstices and equinoctes* when they happen, so you can read all about how and why they occur in past articles. I’ll note that Monday is not the date of the earliest sunrise and latest sunset though; that has to do with the Earth’s orbit being slightly elliptical, so I’ll make a special point of linking to this article last year where I explain why that happens. I’ll also note that some people call this the first day of summer (or winter for those in the south), but I disagree; I tend to think of it as actually the midpoint. You can read about that to your brain’s delight as well.

Earth tilt animation
The Earth's axis stays pointing in one direction in space as it orbits the Sun, so sometimes we're tipped toward the Sun, sometimes away. This is why we have seasons and solstices.

Tfr000/Wikipedia, Creative Commons License

No, instead of spending time on that here, I’d prefer to point out something rather special that led to me wandering down a rabbit hole Sunday night as I researched it: Not only is the solstice Monday, but the Moon is full on Monday as well. That moment occurred at 11:02 UTC (07:02 Eastern; I’ll note it’ll look full all day and probably even Tuesday as well).

A full Moon on the same day as the June solstice (or the December one, for that matter) is relatively rare. As I thought about this Sunday night, I wondered just how rare it was. My first thought was that it probably happens once every 30 years or so, since the full Moon can occur on any day, and there are 30 in June.

But then I realized it’s not that simple. Sometimes in astronomy two cycles can beat together in unusual ways, throwing off what you might expect. So I dug into it. I found a list of solstice full Moon dates on the Farmer’s Almanac website, and perusing the numbers it appears that we get a full Moon on the June solstice roughly every 19 years or so … or multiples thereof.

Nineteen years? That sounded familiar. It took me a few minutes, but then it clicked: That’s the Metonic cycle! Let me explain.

The Moon goes through a full phase of cycles (from full to new and full again) in about 29.53 days. That all by itself is interesting, and I talk about that in the episode of Crash Course Astronomy on the phases of the Moon:

One Earth year is, on average, about 365.24 days long. But there’s a funny coincidence here: 19 years is 6,939.56 days, and that is almost a perfect multiple of 29.53! Nineteen years is almost exactly 235 lunar phase cycles. That means that when you have a full Moon on a given date, 19 years later it’ll be on that same date once again. That’s what’s called the Metonic cycle. This fact has been known for about 2,500 years, which is pretty amazing.

But looking at the Farmer’s Almanac, you see it doesn’t seem to happen every 19 years. Why not?

This is where I really started to dig deep. I looked at leap years, and fractional leftovers between the lunar phase month (called the synodic month) and the Earth’s year, and on and on. That can account for some of the reason the full Moon doesn’t always fall on the same calendar date every 19 years.

Then I realized something: time zones.

Astronomical sites list the times of the solstices and full Moons in Coordinated Universal Time (UTC, similar to Greenwich time). That makes it easy for everyone, since you can just look up how far off your time zone is from that (for example, right now the East Coast of the U.S. is on Eastern Daylight Time, UTC – 4 hours).

But that can mess up the full Moon June solstice cycle. Why? Because the exact moment of the solstice changes year to year, and can even occur on different days! It can be on June 20, 21, or sometimes even 22. If the solstice occurs on June 21 at 23:59, and the full Moon two minutes later, technically they’re on different days!

Worse, that’s UTC. In the U.S., where it’s four to seven hours earlier than UTC, both would occur on the same calendar day. So it’s possible (and even likely) that one place in the world would see a full Moon on the same calendar day as the solstice, and another part of the world wouldn’t. What a mess!

Look at Monday’s solstice: It occurs at 22:34 UTC. For someone a couple of time zones east of the U.K., that means it happens on June 21. For them, they don’t get a full Moon on the day of the solstice. The exact moments of the solstice and full Moon are independent of time on Earth (the solstice occurs at the same moment for everyone on the planet, for example), but because we bin time up into days, that can throw off the days on which we say those events happened. Weird.

Going back to the Farmer’s Almanac, you may notice that while the solstice full Moon doesn’t happen every 19 years, it does appear to have a cycle of multiples of 19. For example, there was one in 1796, then the next in 1834, a gap of 38 years, 2 x 19. Other such gaps can be found. The gaps happen because the full Moon missed the calendar day of the solstice by some hours. Not only that, but that table is for the U.S. East Coast, so it doesn’t work for the whole world.

The root of this problem is using calendar days, which are arbitrary to some extent. There’s an overall 19-year cycle, but because of time zones it can get thrown off. A better way to do this would be to ask, “How often does a full Moon occur within a day of the solstice?,” or better yet within 12 hours before to 12 hours after the moment of the solstice.

In that case, I’d expect the 19-year Metonic cycle to be more obvious. However, looking that up using calendars for the full Moon (like this one) and the solstices (like this one) is difficult and tedious. The best way would be to run the calculations specifically looking for that, which I thought of too late to ask anyone to do for Monday’s events. I’ll leave that as an exercise for the reader.

Anyway, my point is … well, I guess I don’t have a point except that numbers are fun to play with and the cycles in the sky are neither always obvious nor simple to grasp.

But they’re there, and if a full Moon falling on the solstice is interesting enough to people that they go outside and take a look for themselves, then I’m all for it.

So happy full Moon June solstice! Enjoy it, because the next one won’t be for a while—June 21, 2062, in fact … if you use UTC.

*Equinoctes is the actual plural for equinox. Some dictionaries say that’s a bit old-fashioned, and equinoxes is now used, which is fine by me. Languages change over time. But I rather like the way equinoctes sounds, and I like using it. So I do.

June 20 2016 8:45 AM

March … I Mean April… I Mean May 2016 Is the Sixth … I Mean Seventh… I Mean Eighth Temperature Record-Breaking Month in a Row

N.B. If this article sounds familiar, it should. This has been happening so frequently I just copied the post for March April and updated it.

October. November. December. January. February. March. April. And now May.

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For the sixth seventh eighth month in a row, we’ve had a month that has broken the global high temperature record. And not just broken it, but shattered it, blasting through it like the previous record wasn’t even there.

According to NASA’s Goddard Institute for Space Studies, March April May 2016 was the hottest March April May on record, going back 136 years. It was a staggering 1.28°C 1.11°C 0.93° C above average across the planet.* The previous March April May record, from 2010 2014, was 0.92° 0.87° 0.86° above average. This year took a huge jump over that.

Welcome to the new normal, and our new world.

As you can see from the map above, much of this incredible heat spike is located in the extreme northern latitudes. That is not good; it’s this region that’s most fragile to heating. Temperatures soaring to 7° or more above normal means more ice melting, a longer melting season, loss of thinner ice, loss of longer-term ice, and most alarmingly the dumping of billions of tons of fresh water into the saltier ocean which can and will disrupt the Earth’s ability to move that heat around.

What’s going on? El Niño might be the obvious culprit, but in fact it’s only contributing a small amount of overall warming to the globe, probably around 0.1° C or so. That’s not nearly enough to account for this. It’s almost certain that even without El Niño we’d be experiencing record heat.

Most likely there is a confluence of events going on to produce this huge spike in temperature—latent heat in the Pacific waters, wind patterns distributing it, and more.

JMA temperatures
The Japanese Meteorological Agency measured similar temperatures as GISS (though it uses a different baseline for the average), and has May 2016 in a virtual tie for hottest May on record with 2015. Note the trend. See a "pause"? I don't.

Japanese Meteorological Agency

And underlying it all, stoking the fire, is us. Humans. Climate scientists—experts who have devoted their lives to studying and understanding how this all works—agree to an extraordinary degree that humans are responsible for the heating of our planet.

That’s why we’re seeing so many records lately; El Niño might produce a spike, but that spike is sitting on top of an upward trend, the physical manifestation of human induced global warming, driven mostly by our dumping 40 billion tons of carbon dioxide into the air every year.

Until our politicians recognize that this is a threat, and a very serious one, things are unlikely to change much. And the way I see it, the only way to get our politicians to recognize that is to change the politicians we have in office.

That’s a new world we need, and one I sincerely hope we make happen.

*GISS uses the temperatures from 1951–1980 to calculate the average. The Japanese Meteorological Agency uses 1981–2010, which gives different anomaly numbers, but the trend remains the same. Realistically, the range GISS uses is better; by 1981 global warming was already causing average temperatures to rise.

You may have noticed that the actual temperature anomaly for each month over March through May appears to be dropping; 1.28 to 1.11 to 0.93. That may be due to El Niño weakening, but it’s hard to know over such a short time period. Even if the trend continues, I’d bet 2016 will be the hottest year on record.

June 19 2016 9:00 AM

ExoMars Sees Mars

When you spend a lot of time and effort to send a spacecraft to another planet, it’s a nice benchmark when that spacecraft first spots it.

The image above is Mars, as seen by the Trace Gas Orbiter, part of the European Space Agency’s two-pronged ExoMars program (the first mission is the TGO plus Schiaparelli, a lander that will test technologies for future missions, including the 2020 ExoMars rover). TGO and Schiaparelli were launched on March 14 and were about 41 million kilometers from its destination when this shot was taken.

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Mars is only about 6,800 kilometers in diameter, so from that distance it was only a dozen or so pixels across in the camera of the Trace Gas Orbiter. That’s pretty small, which is why it’s hard to see much here. But it shows the camera works! To make the picture a little clearer, here’s a slightly (3 pixel Gaussian) blurred version of it:

Mars
Funny how making it blurry improves it.

ESA/Roscosmos/ExoMars/CaSSIS/UniBE

The image release notes that the Tharsis region of Mars was facing the camera when the shot was taken. Tharsis is a huge area of Mars known for its four massive volcanoes, including Olympus Mons, the largest such beast in the solar system. I poked around and found a Mars picture by Hubble that more or less matches the ExoMars shot:

Hubble Mars
Mars via Hubble in 2003.

NASA, J. Bell (Cornell U.) and M. Wolff (SSI)

That was taken in 2003 and isn’t an exact match, but it’s close. Olympus Mons is the big splotch at the top center, and the dark southern region below it is called Terra Sirenum. Out of curiosity I shrank it to roughly the same size as the ExoMars picture, rotated it, and blurred it a bit to compare them:

Mars
The view from ExoMars (left) and Hubble (right) are similar (the southern ice cap is much more prominent in the 2003 Hubble shot).

ESA/Roscosmos/ExoMars/CaSSIS/UniBE & NASA, J. Bell (Cornell U.) and M. Wolff (SSI)

Not bad. Not exact, but you can see the similarities. This first ExoMars mission will reach Mars in October, and once in orbit the camera (called CaSSIS) will be able to spot objects on the surface as small as 10 meters across—the size of a small house. So expect far more interesting picture than this coming this winter!

June 18 2016 9:00 AM

Blue Origin to Test Rocket Parachute Failure Sunday Morning

Update, June 19, 2016, at 13:00 UTC: The launch was a success! The peak altitude reached was more than 101 kilometers, passing above the Kármán line and into space. The crew capsule deployment looked good, with the two main parachutes slowing the capsule adequately (we’ll know more when the data are analyzed) and the capsule touching down about 10 minutes 30 seconds after launch. One note:The capsule appeared to land too soon, and I'm not sure the retrothrust system activated. We'll know more soon. The rocket itself landed vertically right on target, too.

On Sunday, at approximately 14:15 UTC (10:15 a.m. Eastern time), the private rocket company Blue Origin plans to launch its New Shepard rocket for the fourth time. As with the three previous tests, it’ll launch straight up, deploy the crew capsule, and then come back down vertically. The crew capsule will come back much more slowly, using parachutes to descend gently (and a retrothrust system to make sure the landing isn’t too rough).

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Except this time, the company has rigged it so that only two of the three parachutes will open.

This test is being done on purpose to make sure they can still safely land in the event of single parachute failure. As Blue Origin CEO Jeff Bezos said, “Works on paper, and this test is designed to validate that.”

This should be an exciting test. In a very different move for the company, it has announced that it will be streaming the event live on its website (it starts at 13:45 UTC, a half hour before the launch). I find that very interesting; in general the company has not done that; they release video after the flights, and rarely even announce when the launch tests will be. I wouldn’t say they’re secretive, but they tend not to actively seek publicity.

I have to wonder if the live coverage of SpaceX launches is behind this decision. Obviously, SpaceX has captured the lion’s share of the public’s attention when it comes to rocket launches. SpaceX has carefully cultivated an excellent public outreach effort, and the result is that its launches are watched live by a lot of folks. I imagine Blue Origin wants a piece of that.

They deserve it. New Shepard (named after astronaut Alan Shepard, the first American in space) has launched successfully three times, and each flight has tested different aspects of the process, including a quick restart of the engine only a kilometer above the ground before landing. It’s actually pretty amazing.

What SpaceX is doing and what Blue Origin is doing are, at the moment, very different. SpaceX is launching a very large rocket into orbit, meaning it has to go sideways (usually to the east) very rapidly to go around the Earth. Blue Origin’s flights are suborbital; the rocket goes essentially straight up, past the arbitrary but generally agreed-upon 100-kilometer altitude marking the beginning of space (at that height, there’s almost no air and no drag on the rocket). That’s far easier than going into orbit.

But not easy. Going up that high, releasing a capsule, having that land safely, and landing the rocket itself back down vertically on its tail is incredibly hard. Blue Origin has shown they’re getting the hang of it, though.

And while there’s a good market for suborbital flights (even a few minutes of free fall can be very useful scientifically), the plan is to use the knowledge gained to create a more powerful rocket capable of orbital flight. This is how SpaceX did it with the Falcon 1 rocket that led to the Falcon 9, and Blue Origin has similar ideas. Its BE-4 engine, currently being tested, should have enough oomph to do this. United Launch Alliance, which makes the Atlas and Delta rockets, has partnered with Blue Origin to develop this engine for use with their next generation Vulcan rocket. That’s being created as a competitor for SpaceX’s Falcon series, and I’ll be very interested indeed to see how this goes.

I’ll be getting up early Sunday morning to watch this fourth New Shepard test flight, and live tweeting it, too. Rocket launches are fun and exciting, and these tests are the first steps toward a bigger and better arena for commercial spaceflight. I have a lot of hope for this new chapter in space exploration. A lot, and I think it’s been earned.

There’s an (apocryphal) curse: “May you live in exciting times.” I don’t think it’s a curse. I think it’s the best time to be alive.

June 17 2016 9:00 AM

Another Moon for Earth? Well, Not Really, but It Depends on Your Point of View.

The Earth has one satellite, right? That fact is so solid, we just call it the Moon with a capital M.

But due to a trick of gravity and timing, there are other objects out in space that aren’t really moons but do travel along with Earth through space. I guess “companions” would be a better name.

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One of them was just discovered recently by astronomers: the asteroid 2016 HO3. It’s small, probably 40–100 meters in size, and let me be clear: It orbits the Sun, not the Earth, so I wouldn’t call it a moon. But its orbit is such that it always sticks near the Earth, and from our point of view even seems to go around us!

Here’s how that works. The asteroid was first seen in April 2016 in observations of the sky taken by the Pan-STARRS observatory, designed to look for asteroids and comets that get close to Earth. That’s recent enough that a really good orbit for it is hard to determine, but it turns out it was seen in older observations (those can be found by tracing the orbit backward and checking if any observations of it were archived), providing a much longer baseline and therefore a better orbit.

What they found is really interesting: The orbit of HO3 is very Earth-like! It’s very slightly elliptical, and tilted by about 8° with respect to Earth’s, but the average distance of the asteroid from the Sun is just a hair more than Earth’s, and it takes 365.93 days to orbit the Sun. That’s just 16.6 hours longer than Earth’s 365.24 daylong year!

Because it’s moving on a tilted and elliptical orbit, sometimes it’s a wee bit closer to the Sun and moving a bit faster than Earth, and sometimes it’s a wee bit farther out and moving a bit more slowly. But it never gets closer than about 14 million kilometers from Earth or farther than about 40 million kilometers.

That’s hard to picture, so I made an animation using the JPL Small Body Database Browser. It shows the inner solar system and keeps Earth centered as it and 2016 HO3 orbit the Sun (HO3’s orbit is blue; light blue for when it’s north of (“above”) the Earth’s orbit, and dark blue when it’s south (“below”). As time moves forward, you can see HO3 moving faster and ahead of the Earth, then slowing and lagging behind, but never getting very far away:

So as you can see it’s clearly orbiting the Sun, but never straying far from Earth. If you map its motion relative to Earth, it actually appears to go around us, like a moon! That’s shown in the diagram at the top of this article.

But it gets weirder. Because the orbit is slightly longer than Earth’s, you’d expect it to drift away over many years, lagging behind Earth more and more every year. But that’s not the case! Earth’s gravity tugs on HO3, changing the orbit slightly every time they pass. That keeps HO3’s orbit in line with Earth’s, so it never gets too close or too far away. It’ll be our companion for at least the next few centuries.

If you’re wondering how we’ve missed it all this time, I’ll remind you it’s small and still pretty far away in terms of actual kilometerage. Even at closest approach it’s at about 21st magnitude, or just one-millionth as bright as the faintest star you can see with your unaided eye. It takes a decent telescope to see it at all.

I find things like this delightful. The Universe is so surprising! Due to the law of gravity our solar system is in many ways like a clock, each object like a gear ticking away in time with the others.

But there’s more than fanciful analogies to be had here: Because of its similar orbit, HO3 is moving relatively slowly compared with Earth’s motion through space. That makes it a rather tempting target for a space mission, where how much fuel you need to get from point A to point B depends on their relative motion. HO3 is moving just a few kilometers per second relative to Earth in some parts of it orbit, making it much easier to send a probe there. Or maybe, someday, humans.

How about that? One of the best targets we could hope for, and we just discovered it a few weeks ago. The Universe really is surprising.

June 16 2016 9:00 AM

LIGO Bags Another Binary Black Hole Burst

About 1.4 billion light-years from Earth, two black holes were on a dance of death. One was about 14 times the mass of the Sun; the other eight. For a long time their orbits had been decaying, approaching each other ever more rapidly. And then, finally, so close they were whipping each other around at very nearly the speed of light, they merged. The event was catastrophic, sending out a blast of energy that literally shook the very fabric of the Universe itself.

Eons later, that death cry was seen by astronomers here on Earth. By the time it got here it was vanishingly feeble, but strong enough to shake the sensors in LIGO, the Laser Interferometer Gravitational-Wave Observatory. Two facilities comprise the observatory, one in Livingston, Louisiana, and the other in Hanford, Washington. Each one uses a system of lasers to measure the distance between a set of mirrors, and when the ripples in space-time emanating from the black hole merger passed through the Earth, they changed the distance between mirrors ever so slightly.

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Perhaps I’d better explain. In fact, I already have, when the first event was announced in February 2016:

One of the outcomes of Einstein’s General Relativity theory is that space and time are two facets of the same thing, which we call space-time. There are lots of analogies for it, but you can think of it as the fabric of space, a four-dimensional tapestry (three of space and one of time) in which we are all embedded. Remember, it’s not literally like this; we’re using an analogy. But it’ll help you picture it …
… if a massive object is accelerated, it will cause ripples, waves, to move away from itself as it moves. These are actually ripples in the fabric of space-time itself! Space-time expands and contracts in complicated ways as a wave passes, a bit like how ripples will move out from a rock dropped into a pond, distorting the surface of the water.

In other words, when a massive object accelerates, it emits what’s called a gravitational wave that quite literally stretches and shrinks space. The more massive the object and the higher the acceleration, the more powerful the gravitational wave is, and the more space gets distorted. Most objects in the Universe are way too placid to do this, but when two black holes merge, the masses are high and the acceleration fierce.

Even then, by the time the waves get here (moving at the speed of light across the Universe), the ripples are incredibly tiny. The ripples from this new event, called GW 151226 (for the gravitational wave source detected on Dec. 26, 2015), stretched space by only a factor of about 10-22 by the time they reached Earth. That’s so small it’s hard to imagine, so let me put it this way: If you had a ruler a kilometer long, as a ripple passed through, it would change its length by less than the width of a proton!

Still, that’s measurable! Barely. As I described in my earlier article, LIGO is designed to see incredibly small strains in the fabric of space-time. The biggest problem is noise; in this case the detectors are so sensitive that they can detect molecules of air hitting the mirrors!

It’s taken many years, but last year LIGO was finally made sensitive enough to detect the more powerful gravitational waves passing through it. The first detection, made on Sep. 14, 2015, was from two pretty beefy black holes, roughly 36 and 29 times the mass of the Sun. The event lasted two-tenths of a second.

In this second case, the entire detected event lasted about a full second. As the black holes fell in those last few kilometers, their fierce gravity swung them around faster and faster, causing the gravitational waves to increase in frequency and strength. When sound waves do this, you get a sharp, short “chirp,” and that’s what astronomers call this event, too.

The detection itself is pretty amazing. Automated software checks the signal from the LIGO setup and was the first to notice something was up. It alerted astronomers, who checked to make sure the signal was real. Part of that was looking at the signal from both facilities in Washington and Louisiana, and they both saw it (it was first seen in Louisiana, then in Washington 1.1 milliseconds later; that has to do with the speed of light and the angle to the merging black holes).

signal from the black holes
Top: The signal detected by the LIGO facilities (in red and blue), with the best predicted fit model calculated using Einstein's equations. Bottom: The energy of the signals is hard to see over the noise, but the frequency ramping up into chirps is discernable.

LIGO/VIRGO

Note that in the plot above, a pair of up and down cycles is one orbit of the black holes around each other. These objects combined are 20 times the mass of our entire star, but they were whipping around each other hundreds of times per second before the end.

The exact shape of that signal is predicted by Einstein’s Theory of General Relativity. Using computers, the astronomers then generated literally millions of theoretical signals, comparing them to the observed one. They change the masses of the black holes, as well as many other parameters, giving them a range of values for their masses and distances. In the end, the masses found were 14.2 ± 8.3/3.7 (so as much as 8.3 more and 3.7 less) and 7.5 ± 2.3/2.3 times the mass of the Sun, and the distance roughly 1.4 billion light-years.

This means the black holes were probably created in the usual way. A long time ago, two very massive, hot stars were in orbit around each other. One blew up, expelling its outer layers, and its core collapsed to form a black hole. Sometime after that the second one blew, creating the other black hole. They would have orbited each other stably forever, but Einstein has something to say about that: As they moved, they emitted those gravitational waves. The emission was very weak at first, but it removed energy from the system, and the black holes spiraled every so slightly closer together. As they got closer they moved faster, were accelerated more, and emitted more waves. This was a positive feedback loop, and when they got close enough together, BLOOP! They merged.

The 14 and eight solar mass black holes combined to form a single black hole with 21 times the mass of the Sun.

Of course, 14 + 8 = 22. What happened to the missing mass? That mass was converted into the energy of gravitational waves.

I’m not going to lie to you: Just writing that gave me a chill down the back of neck.

That amount of energy is beyond staggering: It’s equivalent of all the energy the Sun emits over a period of about 15 trillion years. That’s a thousand times the lifetime of the Sun! Or, if you prefer, it’s about the same amount of energy emitted by a billion galaxies like ours over the same time interval as the merger.

And now you can see why astronomers are so excited by this. These are among the most energetic events in the Universe, and until last year we were completely blind to them.

The first event showed we could do it. This second event shows that the age of gravitational wave astronomy is truly here. Mind you, both events were detected just a few months after LIGO became sensitive enough to detect them; many more will be seen, and soon. As data are gathered, we’ll learn more about this entirely new field of astronomy, one completely divorced from the usual detection of electromagnetic waves—light. Certainly, conventional telescopes will help; it’s suspected there may be a brief flash of light accompanying the release of gravitational waves, but it’s not certain. And just on their own, gravitational waves yield a treasure of information.

This is an amazing event. Predicted by esoteric physics a century ago, detected by physics even older than that, we finally have the technology that allows us to hear the faint whispers the results from these deafening roars. And it will allow us understand the universe in a whole new way.

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