"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.
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 extrasolar planets 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.
William Steigerwald | EurekAlert!
Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst
Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy