Artist’s impression shows a view of the surface of the planet Proxima b (Pic: ESO)

By Will Goodbody, Science & Technology Correspondent

Scientists have announced that they have discovered an Earth-like planet orbiting the closest star to our own solar system. It is big news, opening up the prospect that another world, which could potentially harbour life, is right on our doorstep (well in space terms anyway).

What exactly has been found?

For a number of years, astronomers have been busily engaged in a search for extrasolar planets or exoplanets.

These are planets that orbit stars other than our own Sun.

Using instruments attached to telescopes belonging to the European Southern Observatory in Chile and other equipment, one group of astronomers has discovered an exoplanet close to home.

They’ve called it Proxima b, because it is orbiting Proxima Centauri – the closest star to our solar system.

It is the faintest of three stars in the constellation of Centaurus , the other two being Alpha Centauri A and B.

Ok, and what do we know about this new world?

Well, we know a little, but not a lot.

We know it is 1.3 times the size of Earth and orbits its parent star every 11.2 days.

We also know that it is 7 million kilometres from Proxima Centauri, which is 5 per cent of the distance from Earth to the Sun, and a good deal closer than Mercury is to our star.

That sounds very close, but because the star is a red dwarf, it is quite faint in comparison to the Sun.

And so the result is that the temperature range on this newly discovered planet is not all that dissimilar to on Earth.

This means that in theory water could exist on the surface.

That coupled with the strong likelihood that it is rocky, not gaseous, and could have atmosphere (although that is not certain) means it is possible that it has all the ingredients necessary for life to exist.

Wow, that’s pretty unusual isn’t it?

Yes and no.

Organisations like the European Southern Observatory and instruments like the Kepler Space Telescope have already found many exoplanets.

Indeed, Kepler has already found 4,696 candidate exoplanets, 2,326 of which have been confirmed, and 21 of which are less than twice the mass of Earth and situated in the “habitable” or “Goldilocks” zone.

This is a distance where it is not too hot and not too cold for liquid water to exist on the surface, and hence where life could potentially develop.

So the discovery of another exoplanet in the habitable zone of a star – in this case Proxima b – isn’t all that big a deal.

But finding one so close to Earth is.

Artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri (Pic: ESO)

Artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri (Pic: ESO)

How close?

Ok, when talking about space, you must think relatively about it.

And relative to the location of other habitable zone exoplanets that we know about, it is close.

Proxima Centauri is four light years away from our solar system – or 40 trillion kilometres.

That’s a long way, but only a short hop relative to others.

If it is that close, then why did we not know about it before now?

We sort of did, but scientists hadn’t been able to confirm it.

As far back as 2000 initial observations were made of the planet, and its fingerprints were seen in data from around 2009.

A scientific paper proposing its existence was submitted in 2013, but there was still not enough evidence to conclusively support the definitive discovery.

Now after a concerted campaign by a group of 31 astronomers involving some of the most cutting-edge instruments and telescopes in the world, that bar has been met.

The observing campaign was called Pale Red Dot, and involved looking for the tiny back and forth wobble of the star, caused by the gravitational influence of the planet orbiting it.

An extra challenge, however, was that Red dwarfs like Proxima Centauri are slightly active and can emit things called star spots which to the long-distance observer can appear to indicate the presence of an planet.

So the team also had to keep an eye on how bright the star became during the observation period.

How likely is it that there are little green me running around on Proxima b?

The straight answer is that we don’t know.

We do know it is in the habitable zone, which means theoretically water could be present.

But we don’t know to what if any extent it has an atmosphere.

Nor do we have any indication whether or not there was or is liquid water on the surface.

Scientists also think that the conditions on the surface could be strongly impacted by X-ray and ultraviolet flares from the star, which would be much more intense than those on Earth and would make it challenging for life to exist.

What happens next then?

The next thing that researchers hope to establish is the likelihood of there being an atmosphere on this new world.

And the possibility of liquid water on the surface.

Astronomers will be hoping that the planet passes in front of or transits the star when viewed from Earth, which would give us a good view of the atmosphere.

New technology will make that more feasible.

The European Southern Observatory’s Extremely Large Telescope, which should be operational in 2024, will provide a considerably more powerful window into the universe.

Other space based telescopes and satellites, due for launch in the coming years, will also help.

This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. (Pic: ESO)

This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. (Pic: ESO)

Any chance we could go there, seeing as it is close?

The technology doesn’t currently exist to get humans there.

But Project Startshot, backed by Russian billionaire Yuri Milner, is planning to send unmanned high speed nanocraft driven by large sails propelled by lasers from Earth to Alpha Centauri in the coming years.

This discovery may persuade them to change their focus to the closer and considerably more interesting target of Proxima Centauri and its orbiting planet – or possibly even planets.

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