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Potentially habitable super-Earth discovered in our stellar neighborhood

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November 7, 2012

Artist's concept of the HD 40307 planetary system featuring a close-up view of HD 40307g, ...

Artist's concept of the HD 40307 planetary system featuring a close-up view of HD 40307g, which orbits within the habitable zone (Image: J. Pinfield, for the RoPACS network at the University of Hertfordshire)

Due to the masterful efforts of an international team of astronomers, a new super-Earth planet has been discovered within the habitable zone of a star just 42 light years from Earth. Part of a six planetary system, the super-Earth known as HD 40307g has several promising attributes in terms of its ability to support life and because of its relative proximity it may soon be possible to observe the planet optically.

HD 40307 is a quiet K-type dwarf star, a bit smaller and cooler than the Sun, which appears in Earth's southern skies to reside about eight degrees SSE of Canopus, the brightest star in the constellation of Carina. The apparent magnitude of HD 40307 is about 7.1, which means that it is visible in a pair of binoculars.

HD 40307 was known from European Southern Observatory measurements of its radial velocity to have three close-orbiting super-Earths, with orbital periods of 4.3, 9.6, and 20.4 days. The outermost of these planets orbits HD 40307 at a distance of 0.13 Astronomical Unit (AU), or about 12.5 million miles (20 million km), at which distance the solar radiance is considerably stronger than that at Mercury's orbit in our solar system. As yet another of the more than 100 stars found so far that host multiple exoplanets, the discovery was filed away ... but not forgotten.

Advances in analysis methods have recently lead to a re-examination of the radial velocity data of HD 40307.

“We pioneered new data analysis techniques including the use of the wavelength as a filter to reduce the influence of activity on the signal from this star," says Mikko Tuomi of the University of Hertfordshire. "This significantly increased our sensitivity and enabled us to reveal three new super-Earth planets around the star known as HD 40307, making it into a six-planet system.”

The most interesting of the new planets is the one most distant from the star, HD 40307 g. It has a mass at least seven times that of the Earth and orbits its parent star in just under 200 days at a distance of about 0.6 AU (56 million miles or 90 million km), which would put it just inside Venus' orbit. As HD 40307 is smaller and cooler than the Sun, the solar radiance is about 55 percent of that received by the Earth.

HD 40307 g is also distant enough from HD 40307 that it should rotate on its own axis without being tidally locked to its parent star. This suggests a day and night cycle suited to even heating of the planet. Given the right atmospheric conditions, this should allow for liquid water, and even a temperate climate. This is a large planet, but if it has the same average density as does the Earth, it would be about 1.9 times larger in diameter than the Earth. The surface gravity would also be about 1.9 g, a large but not insurmountable gravity.

The maximum separation between HD 40307g and its parent star as seen from Earth is about 50 milliarcseconds, a very small angle, but the upcoming James Webb Space Telescope should easily be able to detect the super-Earth optically. When that is possible, many answers about surface temperature and atmosphere will receive answers. Thus in the not too distant future we may see HD 40307g confirmed as the first solid candidate for extra-terrestrial life.

Source: University of Hertfordshire

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer.   All articles by Brian Dodson
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12 Comments

Amazing stuff. And we've really only just begun searching for these exoplanets. Already we've found a few rocky planets in the habitable zones of their stars.

Stradric
8th November, 2012 @ 07:26 am PST

"The most interesting of the new planets is the one most distant from the star, HD 40307 g. It has a mass at least seven times that of the Earth and..."

"This is a large planet, but if it has the same average density as does the Earth, it would be about 1.9 times larger in diameter than the Earth. The surface gravity would also be about 1.9 g..."

Gravity is proportional to mass. Wouldn't it be at least 7 g?

TJG
8th November, 2012 @ 08:50 am PST

Why is there an emphasis on discovering habitable planets "close" to Earth? Are people planning to leave? Are we looking for new friends? What's up? Curious...

Thanks.

ka

Kim Armstead
8th November, 2012 @ 09:24 am PST

lol only 42 light years away, so if we could travel at the speed of light a newborn sent there, at point of arrival would be 42 years old. our space crafts of today, you would have to live for many thousands of years to make it there alive. its funny that they would say only 42 light years away lol have a nice day regards, Freelance Eng.

Dave Hargraves
8th November, 2012 @ 11:12 am PST

wait... I forgot about the radius...

g=M/r^2

HD's mass = 7xEm

HD's radius = 1.9xEr

HD's g = 7xEm/(1.9xEr)^2

= (7/1.9^2)x(Em/Er^2)

= (7/1.9^2)xEg

=~ 1.94x9.8 m/s^2

...Nevermind.

TJG
8th November, 2012 @ 11:28 am PST

@kim

Half of the first one and all of the second.

Also travel would be easier going to a more nearby colonized planet.

D.O.R.A.
8th November, 2012 @ 11:41 am PST

I bet the inhabitants have very fat legs.

GeoffG
8th November, 2012 @ 12:07 pm PST

@TJG 7 times the mass means 7 times the volume.

V=4/3 X Pi X Radius cubed

If you work it out, this makes the radius 1.9 times that of Earth (as stated above)

Gravitational force is proportional to Mass/Radius².

If the mass is 7 times Earth's then 7 / 1.9² = 1.9

I think the appearance of 1.9 twice in this is a coincidence but my brain's already hurting. :-)

warren52nz
8th November, 2012 @ 12:16 pm PST

Mining! It's all about cold hard cash!

Gregory Gannotti
8th November, 2012 @ 12:35 pm PST

@warren52nz Right! Thanks. All this assumes a density very similar to Earth's. Guess we'll have to wait and see if that's right.

TJG
8th November, 2012 @ 01:02 pm PST

I would love to see the warp drive shown on this site actually work and then be able to travel to these planets, so we wouldn't need an artist rendering. Looking at the universe through giant binoculars isn't as amazing as I'm sure it would be to travel to these places... Hopefully we can put an end to issues on our planet and start moving up and outward to new and bigger things...

Gargamoth
9th November, 2012 @ 02:24 pm PST

@Dave: As you approach the speed of light the time from your point of view will speed up, so it will only take a few years from your perspective to reach the planet. The time on earth will accelerate though and many years will have passed.

Also, scientists are working on technology that warps space rather than goes faster. Within the next few hundred years it may be possible to travel there within hours!

Edgar Walkowsky
15th November, 2012 @ 08:33 pm PST
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