A team of astronomers at Carl Sagan Institute, Cornell University, has produced a reference catalog of spectra and geometric albedos for 19 objects that are representative of the diversity of bodies in our Solar System: eight planets, from rocky to gaseous; nine moons, from frozen to lava spewing; and two dwarf planets (Ceres and Pluto). By comparing observed spectra and albedos of exoplanets to this catalog, astronomers will be able to characterize them. The team’s paper appears in the journal Astrobiology.
An artist’s impression of the Solar System. Image credit: NASA.
“Planetary science broke new ground in the 1970-80s with spectral measurements for solar system bodies,” said lead author Jack Madden, doctoral candidate at the Carl Sagan Institute.
“Exoplanet science will see a similar renaissance in the near future.”
“We use our own Solar System and all we know about its incredible diversity of fascinating worlds as our Rosetta Stone,” added co-author Dr. Lisa Kaltenegger, director of the Carl Sagan Institute.
The new catalog of solar system reference spectra and albedos includes high- and low-resolution versions of the data, which shows astronomers the influence of spectral resolution on an object’s identification.
In addition, it offers examples of how the colors of the 19 solar system models would change if they were orbiting stars other than our Sun.
“With this catalog of light-fingerprints, we will be able to compare new observations of exoplanets to solar system objects — including the gaseous worlds of Jupiter and Saturn, the icy worlds of Europa, the volcanic world of Io and our own life-filled planet,” Dr. Kaltenegger said.
“The technology to directly collect the light from Earth-sized planets around other stars is currently in a clean room waiting to be assembled and trained on the right target,” Madden said.
“With the upcoming launch of the James Webb Space Telescope and the current construction of large ground-based telescopes such as the Giant Magellan Telescope and the Extremely Large Telescope, we are entering a new age of observational ability, so we need a reference catalog of all the planets and moons we already know, to compare these new exoplanet spectra to.”
Albedos of solar system bodies. Image credit: Jack Madden & Lisa Kaltenegger / Carl Sagan Institute, Cornell University.
The catalog will enable scientists to prioritize time-intensive, high-resolution observations of extrasolar planets and moons.
It also offers insights into what kind of worlds won’t be so easy to categorize without high-resolution spectra.
For example, Venus is a rocky planet, but because sunlight reflects from its dense carbon dioxide atmosphere rather than its rocky surface, the colors astronomers observe from such a planet are similar to those of an icy world.
On the outer edge of the habitable zone, rocky exoplanets are likely to have dense atmospheres like Venus.
Such worlds will require long observations to characterize correctly.
“Examining our Solar System from the vantage point of a distant observer is an illuminating exercise,” Madden said.
“By unraveling the mysteries of the objects in the Solar System we can glimpse the secrets of these new worlds we are finding,” Dr. Kaltenegger added.
The catalog of solar system objects’ spectra and geometric albedos is available for download through the Carl Sagan Institute.
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J.H. Madden & Lisa Kaltenegger. A Catalog of Spectra, Albedos, and Colors of Solar System Bodies for Exoplanet Comparison. Astrobiology, published online July 31, 2018; doi: 10.1089/ast.2017.1763
