Daily Archives: August 24, 2016

astronomy, exoplanets, Proxima Centauri b

Proxima Centauri b Found: The Closest Earth-like Planet to Earth

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Long Rumored, Finally Announced

The view from Proxima Centauri b.
An artist’s concept of what Proxima Centauri might look like from the surface of its rocky planet. Courtesy ESO.org.

The rumors have been floating around for weeks about a supposed planet orbiting Proxima Centauri — the closest star to the Sun. That’s a star visible (through a telescope) from the Southern Hemisphere in the constellation Centaurus. It’s part of a triple system, headlined by Alpha and Beta Centauri, with Proxima being the third member.  Proxima is the closest of the three, at a distance of 4.2 light-years.

This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image between the planet and Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.
This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image between the planet and Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.

Today, finally, SOME of the speculation and rumors are put to rest. Astronomers using the European Southern Observatory in Chile have found very strong evidence for a rocky world with a similar mass to our own planet orbiting Proxima Centauri. The parent star is a low-mass M-type star — a red dwarf. It’s highly magnetic and undergoes occasional episodes of flaring and outbursts. That makes it a somewhat volatile star, which may or may not bode well for any life that could exist on the planet.

The planet itself orbits Proxima Cen every 11 days, which means it’s fairly close to its star. However, since Proxima Cen’s surface temperature is somewhat cooler than the Sun’s, the planet orbits in the “Goldilocks zone” where a planet’s surface could support liquid water. That doesn’t mean there IS water there. NOR does it mean there’s life. That is still a subject of very intense debate and discussion, with no clear resolution in sight just yet.

As you can imagine, the idea of a nearby planet with even the possibility of a chance to support life has people quite excited.

How They Found Proxima Centauri b

Data plot of the motion of Proxima Centauri b
This plot shows how the motion of Proxima Centauri towards and away from Earth is changing with time over the first half of 2016. Sometimes Proxima Centauri is approaching Earth at about 5 kilometres per hour — normal human walking pace — and at times receding at the same speed. This gives astronomers a way to calculate its orbit and mass.
Credit:
ESO/G. Anglada-Escudé

Astronomers have spent a long time searching for this planet. At one point, a year or so back, I read reports suggesting that no planet could exist in the system. Other astronomers disagreed. Throughout the first half of this year, a team regularly studied the system with an instrument called the HARPS spectrograph, which dissected the light coming from the system looking for evidence of a planet. It’s mounted on the telescope at ESO’s La Silla observatory in Chile. At the same time, other observatories around the world joined the hunt for the elusive planet.

Planet-hunters use the Doppler effect, the shift in a star’s light spectrum depending on its velocity, to investigate the properties of exoplanets, such as their masses and periods of orbit.

What Do the Data Tell Us?

The results indicate that Proxima Centauri approaches Earth at around normal human walking pace and then recedes at the same speed. Astronomers saw this pattern repeat every 11.2 days. If you know the period, you can ultimately figure out the mass of the planet doing the orbiting. Astronomers worked on this problem and deduced that Proxima Centauri b has about 1.3 times the mass of our own planet and orbits about 7 million kilometers from Proxima Centauri. That’s even closer than Mercury is to our Sun!

There are a great many more details about this discovery that you can read about at ESO’s web site . It’s a pretty momentous discovery, even though we hear about new planets throughout the year now. That’s because it’s so close to us. Now astronomers will spend time trying to learn more about this planet: its atmosphere, details of its surface, etc. Of course, we can’t see it through our current telescopes. It’s just too small and too far away, but using spectral evidence (i.e. clues embedded in the light from the star as it passes through the planet’s atmosphere (if it has one), astronomers will eventually learn more about this place.

Life on Proxima Centauri b? No Evidence YET

Is there life on this newly found world? There’s no way to know yet. First, we have to find out what its atmosphere is like. If it has traces of life-emitted gases, or oxygen (which is one important clue to the existence of life), then that will be one line of evidence. But, we’re not there yet. Figuring out all this will take time.

As this news filters out over the next few days, you’re sure to see lots of screaming headlines written by people who don’t understand the process of discovery. Here are some things to remember: 1) “Earth-like” does NOT mean “identical to Earth”. It means that the planet is rocky and is about Earth’s size. The term “Earth-like” covers a lot of ground (so to speak). 2) Scientists have not discovered life on Proxima Centauri b. They’ve just barely FOUND the planet. Next, they’ll figure out more about it, including whether or not it has water and life. That will take much more careful observing.

It’s a great discovery and now the fun work of figuring out more about this place begins. Stay tuned!