Proxima Centauri might be more sunlike than we thought

October 11, 2016
An artist's illustration depicts the interior of a low-mass star. Such stars have different interior structures than our Sun, so they are not expected to show magnetic activity cycles. However, astronomers have discovered that the nearby star Proxima Centauri defies that expectation and shows signs of a 7-year activity cycle. Credit: NASA/CXC/M.Weiss

In August astronomers announced that the nearby star Proxima Centauri hosts an Earth-sized planet (called Proxima b) in its habitable zone. At first glance, Proxima Centauri seems nothing like our Sun. It's a small, cool, red dwarf star only one-tenth as massive and one-thousandth as luminous as the Sun. However, new research shows that it is sunlike in one surprising way: it has a regular cycle of starspots.

Starspots (like sunspots) are dark blotches on a star's surface where the temperature is a little cooler than the surrounding area. They are driven by magnetic fields. A star is made of ionized gases called plasma. Magnetic fields can restrict the plasma's flow and create spots. Changes to a star's can affect the number and distribution of starspots.

Our Sun experiences an 11-year activity cycle. At the solar minimum, the Sun is nearly spot-free. At solar maximum, typically more than 100 sunspots cover less than one percent of the Sun's surface on average.

The new study finds that Proxima Centauri undergoes a similar cycle lasting seven years from peak to peak. However, its cycle is much more dramatic. At least a full one-fifth of the star's surface is covered in spots at once. Also, some of those spots are much bigger relative to the star's size than the spots on our Sun.

"If intelligent aliens were living on Proxima b, they would have a very dramatic view," says lead author Brad Wargelin of the Harvard-Smithsonian Center for Astrophysics (CfA).

Astronomers were surprised to detect a stellar activity cycle in Proxima Centauri because its interior is expected to be very different from the Sun's. The outer third of the Sun experiences a roiling motion called convection, similar to water boiling in a pot, while the Sun's interior remains relatively still. There is a difference in the speed of rotation between these two regions. Many astronomers think the shear arising from this difference is responsible for generating the Sun's magnetic activity cycle.

In contrast, the interior of a small red dwarf like Proxima Centauri should be convective all the way into the star's core. As a result, it shouldn't experience a regular cycle of activity.

"The existence of a cycle in Proxima Centauri shows that we don't understand how stars' magnetic fields are generated as well as we thought we did," says Smithsonian co-author Jeremy Drake.

The study does not address whether Proxima Centauri's activity cycle would affect the potential habitability of the planet Proxima b. Theory suggests that flares or a stellar wind, both of which are driven by magnetic fields, could scour the planet and strip away any atmosphere. In that case, Proxima b might be like Earth's Moon - located in the , but not at all friendly to life.

"Direct observations of Proxima b won't happen for a long time. Until then, our best bet is to study the star and then plug that information into theories about star-planet interactions," says co-author Steve Saar.

The team detected the activity cycle using ground-based observations from the All Sky Automated Survey combined with space-based X-ray measurements by several missions, including Swift, Chandra, and XMM-Newton. Their results have been accepted for publication in the Monthly Notices of the Royal Astronomical Society and appear online.

Explore further: Planet in star system nearest our Sun 'may have oceans'

More information: B. J. Wargelin et al. Optical, UV, and X-Ray Evidence for a 7-Year Stellar Cycle in Proxima Centauri, Monthly Notices of the Royal Astronomical Society (2016). DOI: 10.1093/mnras/stw2570

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9 comments

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Osiris1
1 / 5 (1) Oct 11, 2016
Politicians have gotten into the act to try now a disinformation campaign in order to forestall a worldwide space race. But it is not gonna work. Too many governments have lied too often, and all it takes is one nation with resources and a need for more space to tell us to 'eff offf' and then go their own way to the stars. That planet is there and all know it.
jonesdave
1 / 5 (1) Oct 11, 2016
Politicians have gotten into the act to try now a disinformation campaign in order to forestall a worldwide space race. But it is not gonna work. Too many governments have lied too often, and all it takes is one nation with resources and a need for more space to tell us to 'eff offf' and then go their own way to the stars. That planet is there and all know it.


And with current technology would take thousands of years to reach. At an absolutely monumental cost. To get to a planet that may be an uninhabitable sh*thole, due to orbiting so close to a flare star. I cannot see any nation, let alone private business, risking a single cent on such an undertaking at this moment in time. Where is the gain in such a costly and long term project, to politicians who never think further ahead than the next election? "Hey people, you'll all thank me for this in 10 000 years!" Be cheaper to terraform Mars.
cantdrive85
1 / 5 (4) Oct 12, 2016
"The existence of a cycle in Proxima Centauri shows that we don't understand how stars' magnetic fields are generated as well as we thought we did," says Smithsonian co-author Jeremy Drake.

Hmmmm...
jonesdave
4 / 5 (4) Oct 12, 2016
"The existence of a cycle in Proxima Centauri shows that we don't understand how stars' magnetic fields are generated as well as we thought we did," says Smithsonian co-author Jeremy Drake.

Hmmmm...


And? Going to tell us where the current is that is powering the evidence-free zone that is the 'electric sun'? Keep telling you, people in glass houses, and all that.
Phys1
not rated yet Oct 12, 2016
@jd
We really have to turn Earth into hell before it becomes more attractive to live on Mars.
There are plenty of empty regions on Earth that look like Mars but at least have an atmosphere.
jonesdave
1 / 5 (1) Oct 12, 2016
@jd
We really have to turn Earth into hell before it becomes more attractive to live on Mars.
There are plenty of empty regions on Earth that look like Mars but at least have an atmosphere.


Aye, 'twas a bit of a sarcastic comment to be honest!
slash
4 / 5 (1) Oct 12, 2016
@jd
We really have to turn Earth into hell before it becomes more attractive to live on Mars.

Unfortunately it is rather easy for us to accomplish just that. All it takes is another world war. And then we will no longer have the facilities required to get there at all.

Better start now than waiting until it's too late.
ROBTHEGOB
5 / 5 (1) Oct 12, 2016
We are already living on a paradise that cannot be equaled anywhere (the Earth). If we cannot take care of this beautiful planet, we will not take care of any other planet we inhabit, and we will be sadly disillusioned in the end.
slash
not rated yet Oct 12, 2016
@ROB:
I wholeheartedly agree. It's delusional to think we can make another planet habitable for our needs when we can't even keep our own habitable. That doesn't mean we shouldn't try, or at least investigate how to do it - but keeping the Earth in a good shape clearly is first priority.

That said, even though I very much respect Musk for his great ideas and his bravery to take on technological challenges, I think it would be smarter to first establish a colony on the moon and learn from the mistakes that will unavoidably happen, before trying something like that on a planet that is effectively out of reach when anything goes awfully wrong and outside help is urgently required.

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