A new study is underway to search for signs of habitability ...
on Earth.
If that sounds like the ultimate waste of science funding,
take a closer look. The project is designed to scan Earth from a distance and
note the evidence for habitability, so that we can better detect that evidence
on distant worlds. In essence, if we want to find life on alien planets, we
have to study a planet known
to host life to determine what clues to look for, scientists say.
The researchers are using the European Space Agency's Venus
Express satellite, in orbit around our neighbor planet, to study Earth from
afar, where it appears smaller than a pixel in the spacecraft's cameras, with
no surface details visible.
"We have initiated the first sustained program of Earth
observation from a distant platform," said David Grinspoon, a Venus Express interdisciplinary
scientist from the Denver Museum of Nature & Science in Colorado. "We want
to know what can we discern about the Earth's habitability based on such
observations. Whatever we learn about Earth, we can then apply to the study of other
worlds."
Since its launch in November 2005, Venus Express has been photographing
Earth from more than 2 million miles (3.5 million kilometers) away with its
Visible and Infrared Thermal Imaging Spectrometer (VIRTIS).
"When the Earth is in a good position, we observe it two or
three times per month," said Giuseppe Piccioni, VIRTIS co-principal
investigator, at the Instituto di Astrofisica Spaziale e Fisica Cosmica in Rome, Italy. The satellite has taken about 40 images of Earth over the past two years.
So far, the project has learned that tracking down signs of
life and livability is not as easy as it sounds.
"We see water and molecular oxygen in Earth's atmosphere,
but Venus also shows these signatures," Piccioni said. "So looking at these
molecules is not enough."
A more subtle signal that could differentiate the two types
of worlds is the so-called red edge – the infrared signal caused by
photosynthetic life. "Green plants are bright in the near infrared," Grinspoon
said.
The Venus Express team is only beginning to analyze the
Earth data to see if our planet's red edge is detectable from a distance. The
researchers also plan to study the signature of Earth when the ocean-sides of
our planet are facing Venus, compared to when the continents are face-on.
The study could prove vital in scientists' ongoing quest to
learn more about the ever-growing catalog of distant worlds we've found in the
galaxy.
Since 1995, astronomers have discovered more than 300 extrasolar
planets. And two new satellite missions — the ESA/French Space Agency COROT
satellite currently in orbit and NASA's Kepler Mission spacecraft set to
launch in March 2009 — bring us closer to the holy grail of exoplanet research:
finding
Earth-sized worlds around other stars.
"We are now on the verge of finding Earth-like planets,"
Grinspoon said.
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