Four Earth-sized planets detected orbiting the nearest sun-like star

August 9, 2017 by Tim Stephens, University of California - Santa Cruz
This illustration compares the four planets detected around the nearby star tau Ceti (top) and the inner planets of our solar system (bottom). Credit: Fabo Feng

A new study by an international team of astronomers reveals that four Earth-sized planets orbit the nearest sun-like star, tau Ceti, which is about 12 light years away and visible to the naked eye. These planets have masses as low as 1.7 Earth mass, making them among the smallest planets ever detected around nearby sun-like stars. Two of them are super-Earths located in the habitable zone of the star, meaning they could support liquid surface water.

The were detected by observing the wobbles in the movement of tau Ceti. This required techniques sensitive enough to detect variations in the movement of the star as small as 30 centimeters per second.

"We are now finally crossing a threshold where, through very sophisticated modeling of large combined data sets from multiple independent observers, we can disentangle the noise due to stellar surface activity from the very tiny signals generated by the gravitational tugs from Earth-sized orbiting planets," said coauthor Steven Vogt, professor of astronomy and astrophysics at UC Santa Cruz.

According to lead author Fabo Feng of the University of Hertfordshire, UK, the researchers are getting tantalizingly close to the 10-centimeter-per-second limit required for detecting Earth analogs. "Our detection of such weak wobbles is a milestone in the search for Earth analogs and the understanding of the Earth's habitability through comparison with these analogs," Feng said. "We have introduced new methods to remove the noise in the data in order to reveal the weak planetary signals."

The outer two planets around tau Ceti are likely to be candidate habitable worlds, although a massive debris disc around the star probably reduces their habitability due to intensive bombardment by asteroids and comets.

The same team also investigated tau Ceti four years ago in 2013, when coauthor Mikko Tuomi of the University of Hertfordshire led an effort in developing data analysis techniques and using the star as a benchmark case. "We came up with an ingenious way of telling the difference between signals caused by planets and those caused by star's activity. We realized that we could see how star's activity differed at different wavelengths and use that information to separate this activity from signals of planets," Tuomi said.

The researchers painstakingly improved the sensitivity of their techniques and were able to rule out two of the signals the team had identified in 2013 as planets. "But no matter how we look at the star, there seem to be at least four orbiting it," Tuomi said. "We are slowly learning to tell the difference between wobbles caused by planets and those caused by stellar active surface. This enabled us to essentially verify the existence of the two outer, potentially habitable planets in the system."

Sun-like stars are thought to be the best targets in the search for habitable Earth-like planets due to their similarity to the sun. Unlike more common smaller stars, such as the red dwarf stars Proxima Centauri and Trappist-1, they are not so faint that planets would be tidally locked, showing the same side to the star at all times. Tau Ceti is very similar to the sun in its size and brightness, and both host multi-planet systems.

A paper on the new findings was accepted for publication in the Astrophysical Journal and is available online.

Explore further: Astronomers discover 'super-Earth' planet orbiting nearby star

More information: Color difference makes a difference: four planet candidates around tau Ceti. arXiv. arxiv.org/abs/1708.02051

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18 comments

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Mark Thomas
5 / 5 (9) Aug 09, 2017
Amazing discovery! The illustration above, showing planets on the inner and outer edges of the habitable zone, may be hinting at the potential for terraforming to play an important role in our future.
rrwillsj
5 / 5 (7) Aug 09, 2017
Information I would want before investing in any colonization effort...

How old is the Tau Ceti system? Is it still in an early planetesimal phase? No sense building another Trump Tower and golf course with big, flaming rocks falling on you all the time.

If the outer two giant-earths have a biologically compatible hydrosphere, that doesn't mean it's compatible with our biology. In addition to the extreme difficulty trying to adapt to the higher gravity.

It remains to see if the inner two planets will turn out to usable much less habitable? And, again, if native biology is less than inimical to ours.
Mark Thomas
5 / 5 (6) Aug 09, 2017
rrwillsj, the unknowns vastly outnumber the knowns, maybe to the point of being ridiculous, so we will have to wait and see how this all plays out for a very long time to get all the answers (assuming it happens at all).

For the time being (living in a pre-warp culture if you are a Star Trek fan), perhaps the biggest advantage this knowledge gives us comes down to improving our sense of perspective. It seems likely to me that we are going to discover far more terraformable worlds close by than those already having our preferred conditions. Once this becomes a hard scientific fact, as opposed to a mere educated guess, it will place the terraforming of Mars in a whole new light. For example, it might be a little easier to get serious about terraforming Mars when we realize living on any near-by planet within many light years will require terraforming too.
Shootist
1 / 5 (4) Aug 09, 2017
Captain Stumpy
5 / 5 (6) Aug 09, 2017
For example, it might be a little easier to get serious about terraforming Mars when we realize living on any near-by planet within many light years will require terraforming too
@Mark
or any good sized moon that can support life for us

of course, i do think terraforming, if it becomes feasible, will be something reserved only for "dead" worlds... if there is any life on it, i don't see it being a good idea
if anything survives the terraforming and learns to exist in our own requirements, it might prove bad for us

this is a long time down the road, though IMHO, especially considering the lack of warp drive and our own inability to currently fix our own planet problems

i would like to see it, but i doubt any of us will live that long
Mark Thomas
5 / 5 (7) Aug 10, 2017
Captain Stumpy, I agree with everything you wrote with the limited exception of terraforming only dead worlds. I agree that worlds with animals and more sophisticated life forms should probably be left alone. On the other hand, if a world supported bacteria only, we probably should be more concerned about dealing with it (as you suggested) than the morality of potentially destroying it. As a practical matter, my guess is bacteria exists in most habitable zone planets. Of course I suspect that is what you meant by "dead" worlds.

TrollBane
5 / 5 (6) Aug 10, 2017
I'm not seeing this on other sites where I would expect to see this publicized.
Captain Stumpy
5 / 5 (5) Aug 10, 2017
Of course I suspect that is what you meant by "dead" worlds.
@mark
pretty much

we already fight tooth and nail to eradicate bacteria, so i don't see leadership currently in the world taking time to consider it "life", though i would surely be intrigued

bacteria that evolves to live on an otherwise barren planet or planetoid will likely be hardy enough to relocate or save in a specialised lab to evolve much like Lenski's lab

that finding could also seriously jump science ahead by large leaps as well

the threat from the bacteria would come if we allowed exposure to our own atmosphere and requirements

but that is all a long way down the road too, and plenty of time to argue about the ethics or feasibility of it all

until then we have to consider that all exploration will be sequestered to our pressurized capsules, ships, domiciles and suits, even when on another planet or planetoid
Captain Stumpy
5 / 5 (5) Aug 10, 2017
I'm not seeing this on other sites where I would expect to see this publicized.
@trollbane
thanks for bringing that up... i checked and found some of the older finds from 2012 (like this: https://www.unive...le-zone/ ) but i haven't seen anything but this PO article

maybe this is just piggybacking on the older finds based upon the newest arXiv release
Fabo Feng, Mikko Tuomi, Hugh R.A. Jones, John Barnes, Guillem Anglada-Escude, Steven S. Vogt, R. Paul Butler
(Submitted on 7 Aug 2017)
https://arxiv.org...08.02051
Pumastar
Aug 10, 2017
This comment has been removed by a moderator.
HeloMenelo
5 / 5 (6) Aug 10, 2017
https://www.centa...age_id=9

a pity the optimism in your link does not gel with the thickness of your skull in understanding science, but then again low ratings, hilarious opinions is your middle name posting from the basement of mommies house ;)
wduckss
5 / 5 (1) Aug 10, 2017
Go back to math. According to the estimates of 2012.y. (https://en.wikipe..._system)
b >2.00 ± 0.80 M⊕, distance 0.105 ± 0.006 AU
c >3.1 ± 1.40 M⊕, distance 0.195 ± 0.011 AU
d >3.60 ± 1.7 M⊕, distance 0.374 ± 0.02 AU
e >4.30 ± 2.1 M⊕, distance 0.552 ± 0.03 AU
f >6.6 ± 3.5 M⊕, distance 1.35 ± 0.09 AU
All the planets are out of the zone that supports life. 4 planets are too close to the star, with their large mass (although the star of 0.78 mass Sun) are very hot body. The mass, f of the possible planet, is over 6.6 M⊕ for distance 1.35 giving a hot body. Life would be possible to have a mass of about 3 M⊕ (and less) at this distance with a star mass of 0.78 MSun.
Da Schneib
not rated yet Aug 10, 2017
@TrollBane, here's the news release from UCSC: https://news.ucsc...ets.html
bobbysius
5 / 5 (1) Aug 10, 2017
Modeling the planets as blackbodies is a good start, but neglects potential atmospheric effects. For instance if Tau Ceti-e has a large albedo and lacks most greenhouse gases, it could be habitable. If Tau Ceti-f has a low albedo and a ton of greenhouse gases that too could be habitable. It's a reasonable assumption that larger mass planets will retain more massive atmospheres, so if F has some CO2, CH4 or H2O, it might be a great place to vacation. E seems to just be too close and too massive.
Nero_Caesar
not rated yet Aug 12, 2017
Amazing discovery! The illustration above, showing planets on the inner and outer edges of the habitable zone, may be hinting at the potential for terraforming to play an important role in our future.


I'm not challenging your opinion, merely hoping you could elaborate a little. Why would terraforming planets on the edge of the habitable zones be beneficial?

TrollBane
not rated yet Aug 12, 2017
With that much debris in the system and the probability of many moons, any civilization capable of reaching Tau Ceti from Earth will establish rotating habitats on asteroids and convenient moons before looking at the investment needed to terraform a super earth planet for the few who are not comfortable living in space. Conditions in said habitats will be closer to Earth like or whatever else is desired than the conditions on a planetary surface. They might do it eventually, but first will come a space civilization.
rrwillsj
not rated yet Aug 14, 2017
Over the years, I have had many discussions with females if the opposite persuasion about this very issue of colonizing off-Earth.

I cannot remember, one single adult woman willing to volunteer to colonize.
Several of the women suggested variations of: First, men have to let themselves be reproductively altered.

That the manly pioneers can be impregnated and carry a fetus to term.
Then, the shell-shocked survivors (if any) asked if they would volunteer to do it again?

I think this is a variation of: If Men were forced to have babies? Abortion would become a Holy Sacrament!
Mark Thomas
not rated yet Aug 23, 2017
Nero_Caesar, at the risk of oversimplifying to put this into a more conventional context, think of these worlds as "fixer-upper" or "handyman special" real estate properties. Not particularly pleasant or even practical to live in now, but with the potential to be nice with a lot of hard work (sweat equity). I agree with Captain Stumpy that terraforming planets outside the solar system is a very long way off, but again, we are talking about developing a more mature perspective of our place in the cosmos.

In the more immediate future, I am convinced we are capable of reaching Mars, and I am far from alone. NASA has said that with proper funding they can and will do it. SpaceX is committed to it. Once we reach Mars the next step is colonization and those efforts will be greatly enhanced by terraforming. It is my strongly-held opinion that terraforming is, or at least should be, in our future.

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