Mars Express to Dip Low Over a Martian Moon

Bad Astronomy
The entire universe in blog form
Dec. 26 2013 8:00 AM

A Fearful Rendezvous for Mars Express

Mars ornament
That actually would make a pretty awesome ornament.

Photo of tree by Tracy Ducasse; Mars by NASA/ESA/Hubble

Ten years ago this Christmas—Dec. 25, 2003—the European Space Agency probe Mars Express took up orbit around the Red Planet. For the past decade it’s been sending back scads of information about Mars and its moons. I’ve written about it many times (see Related Posts below), and the mosaic of the Martian south pole made using Mars Express images was one of my picks for Best Astronomy Photos of 2013.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

On Dec. 29, the probe will make a pretty gutsy move: It will pass just 45 kilometers (27 miles) above the surface of Phobos*, the bigger of the two moons of Mars. Given that Phobos is only about 22 kilometers across, and Mars Express will be zipping along at several kilometers per second, you can see why this is a pretty bold move. It’s passed by Phobos before, but never this close.

Advertisement

It won’t take any pictures, but will relay data about its precise trajectory as it passes Phobos. The gravity of the tiny moon will cause the probe to deviate a bit in its path, and from that the mass of Phobos can be accurately found. Currently, we don’t know the mass exactly, but it appears as if the moon has a very low density, indicating it may be a loosely collected rubble pile, like a giant bag of rocks in space. That can happen if an asteroid or moon suffers repeated low-speed collisions with other space rocks. It shatters in place, like a car windshield when a decent-sized piece of debris hits it.

I’ll write about that once the data are in, analyzed, and reported. In the meantime, here is an extremely cool high-def video of Phobos created using images from Mars Express. This’ll give you a really good look at this weird little moon:

You can see the very odd collection of linear chains of craters across it; these grooves are not well-understood. It’s been theorized they are formed from impacts slamming the moon and creating seismic waves, or that they may have been from chains of debris blasted out from Mars when the planet suffered a major impact. Both of these ideas have big problems with them, and it’s really not at all clear what the heck formed these bizarre features.

Even though Mars and its moons are relatively close by to Earth, there’s a whole lot more we have to learn about them. There are mysteries a-plenty to investigate, and it’s worth our time to look into them. Knowledge is worth it for its own sake, in my not-so-humble opinion, but also it’s simply true that the more we know about the Universe around us, the better we understand our own home world and our place in it.

*“Phobos” means “fear”, hence the post title, but it’s also apropos.

Related Posts



TODAY IN SLATE

The Slatest

Ben Bradlee Dead at 93

The legendary Washington Post editor presided over the paper’s Watergate coverage.

This Scene From All The President’s Men Captures Ben Bradlee’s Genius

Renée Zellweger’s New Face Is Too Real

Sleater-Kinney Was Once America’s Best Rock Band

Can it be again?

Whole Foods Is Desperate for Customers to Feel Warm and Fuzzy Again

The XX Factor

I’m 25. I Have $250.03.

My doctors want me to freeze my eggs.

The XX Factor
Oct. 20 2014 6:17 PM I’m 25. I Have $250.03. My doctors want me to freeze my eggs.
Technocracy

Forget Oculus Rift

This $25 cardboard box turns your phone into an incredibly fun virtual reality experience.

George Tiller’s Murderer Threatens Another Abortion Provider, Claims Free Speech

The Congressional Republican Digging Through Scientists’ Grant Proposals

  News & Politics
Politics
Oct. 22 2014 12:44 AM We Need More Ben Bradlees His relationship with John F. Kennedy shows what’s missing from today’s Washington journalism.
  Business
Moneybox
Oct. 21 2014 5:57 PM Soda and Fries Have Lost Their Charm for Both Consumers and Investors
  Life
The Vault
Oct. 21 2014 2:23 PM A Data-Packed Map of American Immigration in 1903
  Double X
The XX Factor
Oct. 21 2014 3:03 PM Renée Zellweger’s New Face Is Too Real
  Slate Plus
Behind the Scenes
Oct. 21 2014 1:02 PM Where Are Slate Plus Members From? This Weird Cartogram Explains. A weird-looking cartogram of Slate Plus memberships by state.
  Arts
Brow Beat
Oct. 21 2014 9:42 PM The All The President’s Men Scene That Perfectly Captured Ben Bradlee’s Genius
  Technology
Technology
Oct. 21 2014 11:44 PM Driving in Circles The autonomous Google car may never actually happen.
  Health & Science
Climate Desk
Oct. 21 2014 11:53 AM Taking Research for Granted Texas Republican Lamar Smith continues his crusade against independence in science.
  Sports
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.