Emerging Technology from the arXiv

A View from Emerging Technology from the arXiv

How to spot oceans on alien Earths

If we can see the signature of oceans in Earthshine, then we should see it on Earth-like planets elsewhere in the cosmos

  • April 10, 2009

Sunlight scattered from Earth and reflected off the side of the Moon facing away from the Sun is known as Earthshine. The phenomenon has garnered considerable attention in recent years because it can help determine the Earth’s energy budget: take the amount of energy that the Earth reflects away from the total hitting us and you end up with the amount the Earth must absorb. The way that figure is changing is an important factor in climate change.

But exoplanet hunters are interested in Earthshine for another reason–it is a measure of the Earth’s brightness and therefore analogous to observations of an exoplanet.

But Earthshine is not constant over a 24 hour period because specular reflections from oceans are far stronger than those from land. So as the Earth rotates, its Earthshine varies dependng on whether sea or land is facing the Moon. At least, that’s the theory.

Now Sally Langford at the University of Melbourne in Australia and a couple of cobbers have measured this effect for the first time. They say they’ve been able to detect a drop in Earthsine as well as a reddening of the spectrum, as the Indian Ocean swings out of view giving way to Africa’s east coast.

The drop in Earthshine occurs as the ocean gives way to land and the reddening is presumably the result of the well known “red edge” associated with photosynthesis that astronomers have already hypothesised could be used to spot vegetation on other planets.

Now it looks as if they can use variations in the brightness of Earth-like planets to spot oceans too.

Ref: arxiv.org/abs/0904.0845: Photometric Variability in Earthshine Observations

Become an MIT Technology Review Insider for in-depth analysis and unparalleled perspective.
Subscribe today

Uh oh–you've read all five of your free articles for this month.

Insider Premium

$179.95/yr US PRICE

Want more award-winning journalism? Subscribe and become an Insider.

  • Insider Premium {! insider.prices.premium !}*

    {! insider.display.menuOptionsLabel !}

    Our award winning magazine, unlimited access to our story archive, special discounts to MIT Technology Review Events, and exclusive content.

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

    Access to the Magazine archive. Over 24,000 articles going back to 1899 at your fingertips.

    Special Discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

    First Look. Exclusive early access to stories.

    Insider Conversations. Join in and ask questions as our editors talk to innovators from around the world.

  • Insider Plus {! insider.prices.plus !}* Best Value

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus ad-free web experience, select discounts to partner offerings and MIT Technology Review events

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

    Access to the Magazine archive. Over 24,000 articles going back to 1899 at your fingertips.

    Special Discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

  • Insider Basic {! insider.prices.basic !}*

    {! insider.display.menuOptionsLabel !}

    Six issues of our award winning magazine and daily delivery of The Download, our newsletter of what’s important in technology and innovation.

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

You've read of free articles this month.