The Pale Red Dot project has found a planet.
It is a terrestrial planet, orbiting in the formal habitable zone of Proxima Centauri, the nearest star to the Solar System.
This wide-field image shows the Milky Way stretching across the southern sky. The beautiful Carina Nebula (NGC 3372) is seen at the right of the image glowing in red. It is within this spiral arm of our Milky Way that the bright star cluster NGC 3603 resides. At the centre of the image is the constellation of Crux (The Southern Cross). The bright yellow/white star at the left of the image is Alpha Centauri, in fact a system of three stars, at a distance of about 4.4 light-years from Earth. The star Alpha Centauri C, Proxima Centauri, is the closest star to the Solar System.
Proxima Centauri is a low mass red dwarf, and is part of a triple system, the other two stars being α Centauri A and B, which are solar like stars in a close orbit around each other.
3D map of all known stellar systems in the solar neighbourhood within a radius of 12.5 light-years. The Sun is at the centre. The colour is indicative of the temperature and the spectral class — white stars are (main-sequence) A and F dwarfs; yellow stars like the Sun are G dwarfs; orange stars are K dwarfs; and red stars are M dwarfs, by far the most common type of star in the solar neighbourhood. The blue axes are oriented along the galactic coordinate system, and the radii of the rings are 5, 10, and 15 light-years, respectively.
The whole system is a little over 4 light years away, the nearest stars to the Sun, and Proxima is the closest of the three stars.
This image of the sky around the bright star Alpha Centauri AB also shows the much fainter red dwarf star, Proxima Centauri, the closest star to the Solar System. The picture was created from pictures forming part of the Digitized Sky Survey 2. The blue halo around Alpha Centauri AB is an artifact of the photographic process, the star is really pale yellow in colour like the Sun.
α Centauri B was thought to have a planet, but the evidence for that particular planet is looking shaky.
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. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope.
It may have been noise. α Cen A and B were in conjunction, making them hard to observe, but are now separating, and observing campaigns to look for planets around those star are continuing.
ESO researchers, using the radial velocity variability technique, have detected a quite robust signature of a planet with a mass of 1.3 Earth masses, or more, in a 11 day orbit around Proxima Centauri.
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 regular pattern of changing radial velocities repeats with a period of 11.2 days. Careful analysis of the resulting tiny Doppler shifts showed that they indicated the presence of a planet with a mass at least 1.3 times that of the Earth, orbiting about 7 million kilometres from Proxima Centauri — only 5% of the Earth-Sun distance.
Since the Proxima Centauri is almost 1,000 times fainter than the Sun, this puts the putative planet well within the habitable zone of the star, near the inner edge of the zone, but formally inside it.
This infographic compares the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Proxima Centauri is smaller and cooler than the Sun and the planet orbits much closer to its star than Mercury. As a result it lies well within the habitable zone, where liquid water can exist on the planet’s surface.
The planet would most likely be tidally locked to the star, and might either have one face locked to the star (like the Moon to the Earth), or, conceivable, be in a 2:3 tidal lock, like Mercury is with the Sun.
In either case, it is conceivable for this planet to have liquid water on its surface, IF it is has reasonable thickness atmosphere of nice enough composition.
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 is the nearest star to the Sun.
The relative sizes of a number of objects, including the three (known) members of Alpha Centauri triple system and some other stars for which the angular sizes have also been measured with the Very Large Telescope Interferometer (VLTI) at the ESO Paranal Observatory. The Sun and planet Jupiter are also shown for comparison.
It has an Earth like planet orbiting in a nice orbit.
It will be about as easy to characterise as any exoplanet ever.
There really are a lot of exoplanets everywhere, and a lot of them are Earth mass, and a lot of those are in nice orbits.
What a nice Universe.
Next, a nice intense workshop on how to find lots of low mass planets in the habitable zones of lots of stars in the near future.
Should be a fun workshop.
ESO press release – with bonus videos and extra graphics and links.
“A terrestrial planet candidate in a temperate orbit around Proxima Centauri” Anglada-Escude et al. Nature, 25 August, 2016
Two new papers on the topic:
“Proxima Centauri as a Benchmark for Stellar Activity Indicators in the Near Infrared” Paul Robertson et al., ApJ submitted – stellar photometric activity may mimic low amplitude radial velocity variability, and cause false positive signals for candidate planets. This paper looks at multi-band photometry over a long timeline for Proxima Centauri to characterize time scales on which the star varies.
tl;dr there is very little variability on 5-15 day time scales, which makes it very unlikely the planet candidate is a false positive due to stellar variability.
“Effects of Proxima Centauri on Planet Formation in Alpha Centauri” Worth & Sigurdsson, ApJ in press – theory paper by Rachel Worth, my PhD student, on planet formation models for the α Centauri system, taking its putative dynamical history into account.
tl;dr – theoretically there can be planets in the system, few, low mass in close orbits, including around Proxima Centauri. Details could elucidate past history and formation of system.