Three more super-Earths discovered, around star HD 40307

Tuesday, June 17, 2008

More great news with the discovery of three relatively small planets:

A trio of planets called super-Earths has been spotted orbiting a sun-like star, astrophysicists announced today at an international conference in France.

Super-Earths are more massive than Earth but less massive than Uranus and Neptune. Spotting true Earth-sized planets is challenging with current technology, but the presence of super-Earths suggests finding a world like ours is just a matter of time, researchers say.

The team located the trio with the HARPS instrument on the European Southern Observatory's 3.6-meter telescope at La Silla, Chile. They inferred the existence of the planets by noting the worlds' gravitational affects on the parent star's orbit. This method is called the radial velocity, or wobble, technique.

In addition, HARPS astronomers have tallied about 45 new candidate planets with a mass below 30 Earth masses and an orbital period shorter than 50 days. The researchers say the deluge implies one out of every three sun-like stars harbors such planets.

The trio's host star, HD 40307, is slightly less massive than the sun, and is located 42 light-years away, toward the southern Doradus and Pictor constellations. (A light-year is the distance light travels in one year, or about 5.88 trillion miles — 9.46 trillion kilometers.)

that's a lot closer than the last super-Earth discovered, which is located 3000 light-years away. So how big are they and what are their orbits like?

"We have made very precise measurements of the velocity of the star HD 40307 over the last five years, which clearly reveal the presence of three planets," said team member Michel Mayor of the Geneva Observatory in Switzerland.

The smallest of the trio weighs in at 4.2 Earth masses and orbits HD 40307 every 4.3 Earth days, while the largest, with a mass 9.4 times that of Earth, has a 20.4-day orbit. The middleweight is 6.7 Earth masses and has a 9.6-day trek around the star.

Not quite what we'll need for a complete shift of consciousness on space (that requires an Earthlike planet probably within 30 light-years or so), but we're getting closer all the time. Also note that the telescope is only 3.6 metres in diameter - that's a big mirror but certainly nothing close to the largest we have (the smallest on this list is 4.2 m), so this extrasolar planet spotting can be carried out by a lot of instruments we have readily available here on Earth.

Edit: As expected, within a few hours the HD 40307 star system has had its own Wikipedia page created. Here's information on how to find it if you're looking:

Right ascension 05 54 04
Declination -60 01 24

There's quite a discussion going on the article now as well, with quite a few people looking forward to the Kepler Mission launching next year (as am I). One other poster wonders why people don't focus their efforts on "the 50 stars nearest the Earth starting with Proxima Centauri, Sirius etc." There is also an article here from March on a similar subject:
Earth-like rocky planets could be hiding just a few light years away in our closest stellar neighbours. That’s the bold claim by a team of American astronomers at the University of California, Santa Cruz, who also argue that dedicated study of the three-star Alpha Centauri system some four light-years away using existing astronomical techniques could potentially unveil terrestrial exoplanets in as little as five years.

Now, Javiera Guedes and her colleagues argue that the same technique could be applied to our nearest neighbour — the Alpha Centauri star system — to find Earth-like planets. According to them, computer simulations reveal that terrestrial planets are likely to have formed around Alpha Centauri B and could even be within the star’s “habitable zone” where liquid water can exist on a planet’s surface (Astrophys. J. in publication).

“We simulated a proto-planetary disk around Alpha Centauri B over 200 million years and in all simulations were able to form planets of 1-2 Earth masses,” explains Guedes. “Forty percent of these Earths lie in the so-called habitable zone of the star. If these planets do exist, we can observe them using modest resources, such as a one-metre telescope.”

The researchers believe Alpha Centauri B is among the best candidates for finding terrestrial planets thanks to its brightness and position in the sky, which gives a long observational window each year from the southern hemisphere. However, detecting small, rocky planets the size of Earth is challenging because of the relatively small wobbles they induce in their host stars. Up to five years of dedicated observations may be needed to detect any around Alpha Centauri B.


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