Artist's Impression of the Newly Found Exoplanet. The planet, which is only about 5 times as massive as the Earth, circles its parent star in about 10 years. Image courtesy of ESO.org (click to enlarge).
The guys with the scoop: La Silla observatory in Chile. Image courtesy of ESO.org (click to enlarge).
Home of the search: Moonlight over the Andes. Image courtesy of ESO.org (click to enlarge).
Smaller rocky planets in orbits more hospitable to life are expected to be discovered in the next years. La Silla observatory in Chile. Image courtesy of ESO.org (click to enlarge).
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Rocks, ice and an atmosphere: The most Earth like planet yet discovered
Posted: Jan 25, 2006 03:13 pm EST
(Pythom.com) Using a network of telescopes scattered across the globe, including the Danish 1.54m telescope at ESO La Silla (Chile), astronomers discovered a new extrasolar planet significantly more Earth-like than any other planet found so far. The planet, which is only about 5 times as massive as the Earth, circles its parent star in about 10 years.
It is the least massive exoplanet around an ordinary star detected so far and also the coolest. The planet most certainly has a rocky/icy surface. Its discovery marks a groundbreaking result in the search for planets that support life.
A thin atmosphere, like the Earth
The new planet orbits a red star five times less massive than the Sun and located at a distance of about 20,000 light years, not far from the centre of our Milky Way galaxy.
Its relatively cool parent star and large orbit implies that the likely surface temperature of the planet is 220 degrees Centigrade below zero, too cold for liquid water. It is likely to have a thin atmosphere, like the Earth, but its rocky surface is probably deeply buried beneath frozen oceans. It may therefore more closely resemble a more massive version of Pluto, rather than the rocky inner planets like Earth and Venus.
The lowest-mass exoplanet known until now was GJ 876d, which has a probable mass of 7.5 Earth's masses. Unlike the present discovered planet, GJ 876d circles its parent star in about 2 days. It is thus very hot. By comparison, Uranus has about 15 times the mass of the Earth and Neptune, 17, while giant Jupiter weighs as much as 318 earths.
No extrasolar planets were known to exist prior to 1994. To date, we are closing in on 200. The planets are observed through various effects of their presence on their home star.
Smaller rocky planets in orbits more hospitable to life are expected to be discovered in the next years. Telescopes such as Keck in Hawaii strives to increase precision, to allow us to see Earth-mass planets around sun-like stars within the next few years.
Lower-mass objects are very common
"This is only the third extra-solar planet discovered so far through microlensing searches ", said Jean-Philippe Beaulieu (Institut d'Astrophysique de Paris, France), the lead author. "While the other two microlensing planets have masses of a few times that of Jupiter, the discovery of a 5 Earth mass planet - though much harder to detect than more massive ones - is a strong hint that these lower-mass objects are very common. "
Contrary to most exoplanets discovered, OGLE-2005-BLG-390Lb was indeed found using the 'microlensing' technique, based on an effect noted by Albert Einstein in 1912.
We just see the effect of the gravity
"With this method, we let the gravity of a dim, intervening star act as a giant natural telescope for us, magnifying a more distant star, which then temporarily looks brighter ", explained team member Andrew Williams (Perth Observatory, Australia). "A small 'defect' in the brightening reveals the existence of a planet around the lens star. We don't see the planet, or even the star that it's orbiting, we just see the effect of their gravity. "
Such an intervening star causes a characteristic brightening that lasts about a month. Any planets orbiting this star can produce an additional signal, lasting days for giant planets down to hours for Earth-mass planets.
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