Star is crowded by super-Earths

[muriel_volestrangler]

Gliese 667C is a low-luminosity "M-dwarf" star just over one-third the mass of our Sun.

This means its habitable zone can be much closer in before temperatures make liquid water impossible. The team is now confident that three rocky worlds occupy this region at Gilese 667C.

"Their estimated masses range from 2.7 to 3.8 that of the Earth's," Mikko Tuomi told BBC News.
...
"There might, in fact, be more habitable-zone planets in the Universe than there are stars, which makes it much easier for the future space missions to obtain images of these planets.

http://www.bbc.co.uk/news/science-environment-23032467

[lumberjack_jeff]

1. A planet in that zone would be tide-locked like Mercury. n/t

[muriel_volestrangler]

2. Perhaps - but in what ratio?

With the star smaller than the Sun, and the planet being considerably bigger than Mercury, I'd think it wouldn't be 100%. The presence of the other 2 planets close by could also complicate it. And I don't know if anyone would be able to work out the ratio of rotation to orbital period - Mercury's is 3 rotations to 2 orbits, but is that predictable?

[lumberjack_jeff]

4. Thanks for this. I learned something today that I should have learned 35 years ago.

[muriel_volestrangler]

6. If you want a really cool Mercury factoid, try the 'double sunrise'

Double sunrise

Mercury possesses the most eccentric orbit of any planet except Pluto. At its farthest distance from the Sun (aphelion), it lies about 43 million miles (69 million kilometers) away. But when it arrives at its closest point to the Sun (perihelion) it's just under 29 million miles (47 million kilometers) away. So its orbital speed is appreciably greater at perihelion.

Mercury rotates on its axis three times for every two revolutions it makes around the Sun. But when it arrives at perihelion (as it will on September 13) Mercury's orbital velocity will exceed its rotational speed. As a consequence, a hypothetical observer standing on Mercury would see a sight unique in our entire solar system. Over the course of eight days (fours days before perihelion to four days after perihelion), the Sun would appear to reverse its course across the sky, then double back and resume its normal track across the sky.

If our observer were located on that part of Mercury where the Sun were to rise around the time of perihelion, the Sun would appear to partially come up above the eastern horizon, pause and then drop back below the horizon, followed in rapid succession by a second sunrise!

http://www.space.com/268-elusive-mercury-sunrise.html

[longship]

3. Probably, but Mercury's tidal lock is weird.

IIRC, it offers opposite sides to the sun every revolution. That would make for interesting weather patterns.

R&K

[DreamGypsy]

5. Just means different diurnal cycles

There's nothing particularly special about a 24 hour day.

From the article:

"Their orbital periods are 28, 39, and 62 days, which means that they all orbit the star closer to its surface than Mercury in our own system. Yet, the estimated surface temperatures enable the existence of liquid water on them because of the low luminosity and low mass of the star."

I don't know whether HARPS can determine the rotational periods of exoplanets in general, or at all. Depending on the rotation, they could have interesting cycles, just as you point out for Mercury (from Wikipedia):

Mercury is locked so it rotates in a way that is unique in the Solar System. As seen relative to the fixed stars, it rotates exactly three times for every two revolutions it makes around its orbit. As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two years.

My personal speculation is that long days and nights is not a major variable in the conditions for life. I expect there are much greater possible chemical, physical, and biological variations that constitute 'life' than we short-sighted humans can begin to imagine.

[Judi Lynn]

7. Three Potentially Habitable Planets Found Orbiting Gliese 667C

Three Potentially Habitable Planets Found Orbiting Gliese 667C
by Nancy Atkinson on June 25, 2013

A closer look at the previously-studied nearby star Gliese 667C has revealed a treasure trove of planets – at least six – with three super-Earths in the habitable zone around the star. Gliese 667C is part of a triple star system (Gliese 667) and is just over one third of the mass of our Sun. Now that we know there are multiple planets in the so-called Goldilocks zone – a region where liquid water could exist — Gliese 667C might be the best candidate for harboring habitable exo-worlds.

“We knew that the star had three planets from previous studies, so we wanted to see whether there were any more,” said Mikko Tuomi from the University of Hertfordshire in the UK, one of the astronomers who led the new study of Gliese 667C. “By adding some new observations and revisiting existing data we were able to confirm these three and confidently reveal several more. Finding three low-mass planets in the star’s habitable zone is very exciting!”

Tuomi, along with Guillem Anglada-Escudé of the University of Göttingen, Germany looked at existing radial velocity data from the HARPS spectrograph at ESO’s 3.6-metre telescope in Chile. The team said they are extremely confident on the data on the first five planets, while the sixth is tentative, and a potential seventh planet even more tentative.

More:
http://www.universetoday.com/103131/three-potentially-habitable-planets-found-orbiting-gliese-667c/#ixzz2XGa7FdTQ