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Astronomers have confirmed the rumors - Proxima Centauri, the closest star to our solar system, harbours an alien world that may turn out to be an Earth 2.0!
OUT OF THIS WORLD | What's Up In Space Special Edition

Possible Earth 2.0 found around closest neighbouring star


Scott Sutherland
Meteorologist/Science Writer

Wednesday, August 24, 2016, 1:40 PM - After last week's teaser about a newly-discovered exoplanet, astronomers have confirmed the rumors - Proxima Centauri, the closest star to our solar system, harbours an alien world that may turn out to be an Earth 2.0!

Welcome to our new neighbour, Proxima b!

Astronomers have discovered many alien worlds so far, with over 3,000 exoplanets confirmed over the past 20 years or so. On Wednesday, however, the participants in the Pale Red Dot campaign announced something unique: the closest extra-solar planet ever discovered, and the closest that will likely ever be discovered, because it orbits around Proxima Centauri, the closest stellar neighbour to our solar system.


Rocky planet Proxima b orbiting around red dwarf Proxima Centauri. Credit: ESO/M. Kornmesser

QUICK FACTS

• It's the closest exoplanet ever discovered
• It's most certainly a rocky world
• It's a bit bigger than Earth
• It orbits every 11.2 days, in the star's habitable zone
• All of this adds up to a potentially "Earth-like" world
• It may not be alone
• We may sent probes there within this lifetime

"The first hints of a possible planet were spotted back in 2013, but the detection was not convincing," Guillem Anglada-Escudé, the lead scientist for Pale Red Dot, from Queen Mary University of London, said in a European Southern Observatory press release. "Since then we have worked hard to get further observations off the ground with help from ESO and others. The recent Pale Red Dot campaign has been about two years in the planning."

"I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot campaign," Anglada-Escudé explained. "The first 10 were promising, the first 20 were consistent with expectations, and at 30 days the result was pretty much definitive, so we started drafting the paper!"

Not only has this newfound planet, now named Proxima b, become the closest extra-solar planet to us, but it is an ideal find!

At just 30 per cent more massive than Earth, it is likely only slightly larger than our world, and based on what we've already seen for worlds like this from other discoveries, it is most certainly a rocky planet. Also, based on simulations of the red dwarf star's mass and luminosity, and the fact that Proxima b travels around the star every 11.2 days, this alien world is inside Proxima Centauri's habitable zone - that band of space around the star where it's just warm enough for liquid water to exist on the planet's surface!


A comparison of the orbit of Mercury around our Sun with Proxima b's orbit around Proxima Centauri. Credit: ESO/M. Kornmesser/G. Coleman

While this does not guarantee that life exists on the planet, Proxima b's location in the habitable zone does increase the likelihood that it harbours life as we know it.

One thing is clear, however, if there is life on Proxima b, it experiences something totally different to what we experience here on Earth. Since the planet is so close to the star, Proxima Centauri would appear as a large, dull red-orange orb in Proxima b's sky, roughly three times larger than the Sun appears in our sky here on Earth.


A hypothetical view from the surface of Proxima b. Proxima Centauri appears very large in the planet's sky, while distant binary stars Alpha Centauri A and B also shine as tiny disks. Credit: ESO/M. Kornmesser

Also, due to Proxima b's close orbit, the planet is very likely tidally-locked to the star - that is, the same side of the planet always faces the star, similar to how the Moon always shows the same face to us as it orbits Earth. If Proxima b has an atmosphere and water, this would very likely produce what's referred to as an "eyeball Earth," with the star-lit side of the planet having a scorched circle of desert in the middle, as the pupil, surrounded by an "iris" of water and habitable land, and the rest of the planet, the edges of the star-lit side and the entire dark-side, covered in a white sheet of ice.

Based on studies of Proxima b, there is a chance that it orbits its star more like Mercury does our Sun, completing three revolutions for every two orbits it completes around Proxima Centauri. This would provide slightly more even heating around the planet's surface, and thus more habitable land if conditions allow for it.

Fool us once...

Quite infamously, perhaps, a supposed planet discovered around the Sun-like star Alpha Centauri B, which was the subject of a public naming campaign, was subsequently shown to be simply an artifact of the activity of the star, and it did not actually exist, after all. While it's certainly possible that Proxima b could turn out to be a similar artifact, the astronomers put the odds of it being a "false positive" at only around 1 chance in 10 million, thus there is a very, very high probability that this planet is real.

The reason for this is that the processes of finding these planets have been different.

The "false positive" for Alpha Centauri Bb was spotted after heavy processing of the data, to remove a multitude of noise from the signal, which left behind a tiny blip that was thought to be a planet. The recurring signal for Proxima b, on the other hand, has been observed for some time and has survived multiple attempt to by astronomers who have tried to make the signal vanish. Try as they might, though, this recurring signal has persisted, and the efforts of the Pale Red Dot campaign were only the latest, and most thorough attempt.

If what the astronomers are seeing as Proxima b turns out not to be a planet, it would be something else entirely new to us.

Does Proxima b harbour life?

With the size and luminosity of Proxima Centauri and Proxima b's distance fro the star, the astronomers have estimated that the planet receives somewhere around 65 per cent of the light and heat that Earth receives from the Sun.


A comparative look at Proxima Centauri viewed from
Proxima b, and The Sun, as viewed from Earth.
Credit: ESO/G. Coleman

According to their simulations, this would give an average temperature for the planet of around -40oC. On Earth, if the planet did not have an atmosphere, the temperature would be an average of -18oC. The natural greenhouse effect of the atmosphere raises the global temperature by around 33 degrees, maintaining a more balmy average of +15oC. If Proxima b had an Earth-like atmosphere and oceans, a similar rise in temperatures would still keep it sub-zero, however Proxima b is a bit more massive than Earth. Thus, the stronger gravity would allow for a slightly thicker atmosphere than we have here.

With a similar, but thicker atmosphere to Earth's, Proxima b could enjoy a similar, if slightly cooler, climate, which would certainly favour the development of life.

Another factor in this, however, is the star, Proxima Centauri. Red dwarf stars are the longest-lived of any type of star, but they are also volatile, blasting out immense flares that can bombard the close orbiting planets that cluster around them. According to the ESO team, observations of Proxima Centauri show that it is quiet by comparison, with an activity level more like our Sun. Thus, the environment around this particular red dwarf may be more hospitable than around your average dwarf star.

Even so, since the planet would be dealing with more x-ray bombardment, being so close to the star (compared to Earth), it would need a strong magnetic field and a thick atmosphere to protect the surface. The thick atmosphere may not be a problem, depending on the conditions when the planet formed, however since it would rotate very slowly, it would be difficult for the planet to maintain a strong magnetic field, to capture and deflect high energy charged particles, and prevent them from stripping away the atmosphere.

Studies have already delved into these questions for Proxima b, and one of the key conclusions is that determining whether or not a planet is habitable is very difficult, especially when you only have limited information about it and how it formed and evolved over time.

Can we visit this planet?

One hard fact for those of us raised on science fiction is that, even though Proxima Centauri is the closest star to our Sun, it still lies at a distance of around 40 trillion kilometres away. To put that into perspective, the distance to Pluto is 7.5 billion kilometres, and it took roughly 10 years for NASA's New Horizons spacecraft to reach it. That's without having any humans on board (along with all the necessary baggage needed when we travel, like food, water, air, etc). Even so, with Proxima Centauri located over 5,200 times farther away, it would take at least 50,000 years for a spacecraft like New Horizons to arrive there.

Thus, with our current technology, undertaking such a journey would be a daunting task, to say the very least. We should probably just focus on staying here on Earth for awhile longer.

We do have a chance to survey Proxima Centauri and Proxima b, however, thanks to the Breakthrough Starshot program. Proposed by Russian internet investor and science philanthropist Yuri Milner, and supported by astrophysicist Stephen Hawking, Starshot seeks to propel tiny spacecraft, the size of a computer chip, using a laser beam, which could arrive at Alpha Centauri in around 20 years.

According to Pete Worden, the former director of NASA AMES Research Center, who is leading the Breakthrough Starshot program, with Proxima Centauri only a few degrees off from Alpha Centauri, Starshot could easily be re-aimed to this destination instead, or probes could be sent to both Alpha Centauri and Proxima Centauri.

"From the beginning, we had looked at sending nanoprobes - hundreds of them - to both star systems", Worden said during Wednesday's press conference. "What this now tells us is that we know that there is at least one very interesting target that's within range of our proposed system."

So, while it wouldn't be us travelling there, we could at least send representatives that could transmit images and data back to us.

That is the value of Proxima b, and perhaps the most important part of this discovery. Even if this exoplanet turns out to be a barren rock, it's still the closest exoplanet we know about. It's fast orbit around a star only 4.2 light years away, provides an incredibly useful target for research into how planets and star systems form and evolve, and it provides a great contrast to our own solar system.

Other neighbours?

Another interesting tidbit of information that has come from Wednesday's announcement is the fact that Proxima b may have siblings!

According to the astronomers who discovered Proxima b, the data collected reveals a second signal, with a period of around 20 days, which has persisted alongside the signal for Proxima b. While this signal is not strong enough for a confident identification as a planet at this time, the team is confident that Proxima Centauri is a "multi-planet system."

Future observations - perhaps with the upcoming James Webb Space Telescope or the Transiting Exoplanet Survey Satellite - could confirm at least one more planet around Proxima Centauri, if not more!

What's next?

"Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analogue and succeeding has been the experience of a lifetime for all of us," Anglada-Escudé said in the press release. "Many people’s stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next..."

Sources: ESO | Pale Red Dot | Planetary Habitability Laboratory

Watch below: Proxima b is now the closest exoplanet ever! The ESO summarizes the discovery of this world, which orbits neighbouring red dwarf star, Proxima Centauri.

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