Pic From Mars Altered to Look More Like Home

The entire universe in blog form
April 6 2013 8:00 AM

Blue Skies Smiling at…Mars?

This is awesome and weird and cool and actually useful: A mosaic of Mount Sharp—the five-kilometer (3-mile) high mountain in the center of Gale Crater—taken by the Mars Curiosity rover has had its white balance altered to make the lighting conditions look as they would on Earth:

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!  

Blue sky on Mars
Your eyes are not playing tricks on you. Your brain is. Click to rayleighscatternate.

Image credit: NASA/JPL-Caltech/MSSS

Mars with a blue sky is a bit disconcerting (here’s a picture of a piece of Mount Sharp with the colors balanced correctly). But this is more than just a (ahem) curiosity. Geologists train under the lighting conditions we have here on Earth, but the Sun is fainter on Mars, and the sky a different, butterscotch color. That can trick the brain, making it harder to spot subtle details or see features that would be obvious here on Earth. So sometimes scientists fiddle with the pictures a bit to make them easier to analyze.


I’ve done this many times myself with Hubble images. There might be faint material surrounding a bright star, and it’s hard to see because the star is blasting away. Astronomers commonly change the contrast from a linear scale—where something that’s twice as bright is shown that way—to a logarithmic scale, which goes by factors of ten. So an object 10 times as bright as another “in real life” is scaled to only look twice as bright. A factor of 100 is displayed as a factor of three. It’s actually more complicated than this, dealing with greyscales and such, but that’s the idea.

It really helps in picking out faint sources in an image, and it’s probably because it mimics better the way our eyes see. You’re sensitive to huge scales of brightness. The full Moon is the brightest object you can safely see in the sky (the next brightest is the Sun), and the full Moon is roughly 30 million times brighter than the faintest star you can see. Scaled logarithmically, that’s only a factor of about 7.5. Much better.

And that’s how your eyes work, more or less. If something twice as bright looked twice as bright to you, you’d hardly see any contrast at all. Our other senses are that way, actually. We use decibels for sounds, for example, and that’s a log unit too.

Anyway, fiddling with images is a tried and true method to help scientists understand what we’re seeing. You have to be careful and not see something that isn’t there, but getting trained to do that is easier than trying to see something you just can’t see.



Medical Examiner

The Most Terrifying Thing About Ebola 

The disease threatens humanity by preying on humanity.

I Bought the Huge iPhone. I’m Already Thinking of Returning It.

Scotland Is Just the Beginning. Expect More Political Earthquakes in Europe.

Students Aren’t Going to College Football Games as Much Anymore

And schools are getting worried.

Two Damn Good, Very Different Movies About Soldiers Returning From War

The XX Factor

Lifetime Didn’t Think the Steubenville Rape Case Was Dramatic Enough

So they added a little self-immolation.


Blacks Don’t Have a Corporal Punishment Problem

Americans do. But when blacks exhibit the same behaviors as others, it becomes part of a greater black pathology. 

Why a Sketch of Chelsea Manning Is Stirring Up Controversy

How Worried Should Poland, the Baltic States, and Georgia Be About a Russian Invasion?

Trending News Channel
Sept. 19 2014 1:11 PM Watch Flashes of Lightning Created in a Lab  
  News & Politics
Sept. 20 2014 11:13 AM -30-
Business Insider
Sept. 20 2014 6:30 AM The Man Making Bill Gates Richer
Sept. 20 2014 7:27 AM How Do Plants Grow Aboard the International Space Station?
  Double X
The XX Factor
Sept. 19 2014 11:33 AM Planned Parenthood Is About to Make It a Lot Easier to Get Birth Control
  Slate Plus
Slate Picks
Sept. 19 2014 12:00 PM What Happened at Slate This Week? The Slatest editor tells us to read well-informed skepticism, media criticism, and more.
Brow Beat
Sept. 20 2014 3:21 PM “The More You Know (About Black People)” Uses Very Funny PSAs to Condemn Black Stereotypes
Future Tense
Sept. 19 2014 5:03 PM White House Chief Information Officer Will Run U.S. Ebola Response
  Health & Science
Bad Astronomy
Sept. 20 2014 7:00 AM The Shaggy Sun
Sports Nut
Sept. 18 2014 11:42 AM Grandmaster Clash One of the most amazing feats in chess history just happened, and no one noticed.