Scientists Develop New Method to Find Alien Oceans, Earth-like Planets (w/Videos)

May 26, 2009 By Bill Steigerwald
This narrow-angle color image of the Earth, dubbed 'Pale Blue Dot', is a part of the first ever 'portrait' of the solar system taken by Voyager 1. The spacecraft acquired a total of 60 frames for a mosaic of the solar system from a distance of more than 4 billion miles from Earth and about 32 degrees above the ecliptic. From Voyager's great distance Earth is a mere point of light, less than the size of a picture element even in the narrow-angle camera. Earth was a crescent only 0.12 pixel in size. Coincidentally, Earth lies right in the center of one of the scattered light rays resulting from taking the image so close to the sun. This blown-up image of the Earth was taken through three color filters -- violet, blue and green -- and recombined to produce the color image. The background features in the image are artifacts resulting from the magnification. Credit: NASA JPL

(PhysOrg.com) -- Since the early 1990s astronomers have discovered more than 300 planets orbiting stars other than our sun, nearly all of them gas giants like Jupiter. Powerful space telescopes, such as the one that is central to NASA's recently launched Kepler Mission, will make it easier to spot much smaller rocky extrasolar planets, or exoplanets, more similar to Earth.

Astronomers have found more than 300 alien (extrasolar) worlds so far. Most of these are gas giants like , and are either too hot (too close to their star) or too cold (too far away) to support life as we know it.

Sometime in the near future, however, astronomers will probably find one that's just right - a planet with a solid surface that's the right distance for a temperature that allows -- an essential ingredient in the recipe for life.

But the first picture of this world will be just a speck of light. How can we find out if it might have liquid water on its surface? If it has lots of water - oceans - we are in luck.

This video is not supported by your browser at this time.
These two videos from EPOXI show the moon transiting (passing in front of) Earth. They are observed at different light wavelengths, which is why differences in details are visible. The first version uses a red-green-blue filter; the second, an infrared-green-blue. The first pictures of an Earth-like extrasolar planet will not be this detailed. Instead, the images will be more like the Voyager picture of Earth as a single point of light (below). Videos credit: Donald J. Lindler, Sigma Space Corporation/GSFC; EPOCh/DIXI Science Teams

NASA-sponsored scientists looking back at Earth with the Deep Impact/EPOXI mission have developed a method to indicate whether Earth-like extrasolar worlds have oceans.

"A 'pale blue dot' is the best picture we will get of an Earth-like extrasolar world using even the most advanced telescopes planned for the next couple decades," said Nicolas B. Cowan, of the University of Washington. "So how do we find out if it is capable of supporting life? If we can determine that the planet has oceans of liquid water, it greatly increases the likelihood that it supports life. We used the High Resolution Imager telescope on Deep Impact to look at Earth from tens of millions of miles away -- an 'alien' point of view -- and developed a method to indicate the presence of oceans by analyzing how Earth's light changes as the planet rotates. This method can be used to identify extrasolar ocean-bearing Earths."

Cowan is lead author of a paper on this research appearing in the August 2009 issue of the Astrophysical Journal. Our planet looks blue all the time because of Rayleigh scattering of sunlight by the atmosphere, the same reason that the sky appears blue to us down on the surface, points out Cowan. "What we studied in this paper was how that blue color changes in time: oceans are bluer than continents, which appear red or orange because land is most reflective at red and near-infrared wavelengths of light. Oceans only reflect much at blue (short) wavelengths," said Cowan.

This video is not supported by your browser at this time.
These two videos from EPOXI show the moon transiting (passing in front of) Earth. They are observed at different light wavelengths, which is why differences in details are visible. The first version uses a red-green-blue filter; the second, an infrared-green-blue. The first pictures of an Earth-like extrasolar planet will not be this detailed. Instead, the images will be more like the Voyager picture of Earth as a single point of light (below). Videos credit: Donald J. Lindler, Sigma Space Corporation/GSFC; EPOCh/DIXI Science Teams

The maps that the team created are only sensitive to the longitudinal (East - West) positions of oceans and continents. Furthermore, the observations only pick out what is going on near the equator of Earth: the equator gets more sunlight than higher latitudes, and the EPOXI spacecraft was above the equator when the observations were taken. These limitations of viewing geometry could plague observations of extrasolar planets as well: "We could erroneously see the planet as a desert world if it had a nearly solid band of continents around its equator and oceans at its poles," said Cowan.

Other things besides water can make a planet appear blue; for example, in our solar system the planet Neptune is blue due in part to the presence of methane in its upper atmosphere. "However, a Neptune-like world would appear as an unchanging blue using this technique, and again it's the changes in the blue color that reveal oceans to us," said Cowan. "There are some weird scenarios you can dream up that don't involve oceans but would lead to varying patches of blue on a planet, but these are not very plausible."

"A spectrum of the planet's light that reveals the presence of water is necessary to confirm the existence of oceans," said Drake Deming, a co-author of the paper at NASA's Goddard Space Flight Center in Greenbelt, Md. Instruments that produce a spectrum are attached to telescopes and spread out light into its component colors, like a prism separates white light into a rainbow. Every element and molecule emits and absorbs light at specific colors. These colors can be used like a fingerprint to identify them. "Finding the water molecule in the spectrum of an extrasolar planet would indicate that there is water vapor in its atmosphere, making it likely that the blue patches we were seeing as it rotates were indeed oceans of liquid water. However, it will take future large space telescopes to get a precise spectrum of such distant planets, while our technique can be used now as an indication that they could have oceans," said Deming. The technique only requires relatively crude spectra to get the intensity of light over broad color ranges, according to the team.

NASA's Deep Impact made history when the mission team directed an impactor from the spacecraft into comet Tempel 1 on July 4, 2005. NASA recently extended the mission, redirecting the spacecraft for a flyby of comet Hartley 2 on Nov. 4, 2010. EPOXI is a combination of the names for the two extended mission components: a search for during the cruise to Hartley 2, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact eXtended Investigation (DIXI). The University of Maryland is the Principal Investigator institution, leading the overall EPOXI mission and DIXI. NASA Goddard leads the EPOCh investigation. NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages EPOXI for NASA's Science Mission Directorate, Washington. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.

More information: The paper is scheduled to be published in the August 2009 edition of Astrophysical Journal.

Provided by JPL/ (news : web)

Explore further: Quest for extraterrestrial life not over, experts say

add to favorites email to friend print save as pdf

Related Stories

Deep Impact Films Earth as an Alien World

Jul 18, 2008

(PhysOrg.com) -- NASA's Deep Impact spacecraft has created a video of the moon transiting (passing in front of) Earth as seen from the spacecraft's point of view 31 million miles away. Scientists are using ...

Deep Impact Begins Hunt for Alien Worlds

Feb 08, 2008

NASA's Deep Impact spacecraft is aiming its largest telescope at five stars in a search for alien (exosolar) planets as it enters its extended mission, called Epoxi.

Deep Impact 'celebrates' New Year's Eve with Earth flyby

Jan 02, 2008

Earth Flyby and Moon Pics Mark Start of Journey to Hartely 2 This New Year's Eve the University of Maryland-led Deep Impact team will again celebrate a holiday in a way that few can match, when their Deep ...

NASA Sends Spacecraft on Mission to Comet Hartley 2

Dec 14, 2007

NASA has approved the retargeting of the EPOXI mission for a flyby of comet Hartley 2 on Oct. 11, 2010. Hartley 2 was chosen as EPOXI's destination after the initial target, comet Boethin, could not be found. ...

Earth: The Lone Pale Blue Dot?

Nov 02, 2006

A recent photo from the Cassini spacecraft shows the mighty planet Saturn, and if you look very closely between its wing-like rings, a faint pinprick of light. That tiny dot is Earth bustling with life as we ...

Recommended for you

Quest for extraterrestrial life not over, experts say

Apr 18, 2014

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

Continents may be a key feature of Super-Earths

Apr 18, 2014

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Exoplanets soon to gleam in the eye of NESSI

Apr 18, 2014

(Phys.org) —The New Mexico Exoplanet Spectroscopic Survey Instrument (NESSI) will soon get its first "taste" of exoplanets, helping astronomers decipher their chemical composition. Exoplanets are planets ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

Archivis
5 / 5 (2) May 26, 2009
"There are some weird scenarios you can dream up that don't involve oceans but would lead to varying patches of blue on a planet, but these are not very plausible."
---------------------------------------------------

Yep... Planet of Smurfs... LOL :)
gmurphy
not rated yet May 27, 2009
or, for example, the blue hue of Uranus, which is caused by the absorption of red light by methane in the upper atmosphere
pookawiz
not rated yet May 27, 2009
Wow! And I thought Uranus was blue because it was COLD!

More news stories

Another fireball explodes over Russia

Why does Russia seem to get so many bright meteors? Well at 6.6 million square miles it's by far the largest country in the world plus, with dashboard-mounted cameras being so commonplace (partly to help ...

ISEE-3 comes to visit Earth

(Phys.org) —It launched in 1978. It was the first satellite to study the constant flow of solar wind streaming toward Earth from a stable orbit point between our planet and the sun known as the Lagrangian ...

NASA's MMS observatories stacked for testing

(Phys.org) —Engineers at NASA's Goddard Space Flight Center in Greenbelt, Md., accomplished another first. Using a large overhead crane, they mated two Magnetospheric Multiscale, or MMS, observatories – ...