Another of our Sun’s closest neighbours has been found to be home to a “super-Earth” scale planet.
Barnard’s Star, named after American astronomer Edward Emerson Barnard, is a low-mass M-class red dwarf star. As I’ve noted in previous discussions of exoplanets, red dwarf stars are the most common type of star in our galaxy, believed to account for around 70% of all stars. They can be quite volatile in nature and prone stellar flares, meaning any planets in close proximity to them are unlikely to be very habitable.
But Barnard’s Star is somewhat unusual; while it is estimated to be between two and three times older than the Sun, it has a relatively low level of activity. It also has the fastest radial (side-to-side) motion of any visible star in the night sky – something that might indicate the presence of a large planet orbiting it, causing it to wobble in its spin.
Over the years, astronomer have attempted to use the star’s radial motion to try to establish if it is the result of a planet, and in 2015, instruments used by the European Southern Observatory and the Keck Observatory suggested there could be a very large planet with an orbital period of about 230 days.
More recently, the Red Dots and CARMENES campaigns, which were responsible for the discovery of a planet orbiting our nearest stellar neighbour, Proxima B (see here for more), reviewed the data gathered from multiple sources that have studied Barnard’s Star in an attempt to ascertain whether there is one or more planets orbiting Barnard’s Star.
For the analysis we used observations from seven different instruments, spanning 20 years, making this one of the largest and most extensive datasets ever used for precise radial velocity studies. The combination of all data led to a total of 771 measurements.
– Ignasi Ribas, director of the Monstec Astronomical Observatory, and study lead
The results of this work appear to confirm that there is a planet – referred to as Barnard’s Star b – is orbiting the star roughly one every 233 terrestrial days. It has a mass of at least 3.2 times that of Earth, putting it if the category of either a “super-Earth” or a “mini-Neptune”. It is some 0.4 AU (0.4 times the distance between the Earth and the Sun) from its parent.
Because of Barnard’s Star low mass and brightness, the planet only receives about 2% of the energy that the Earth receives from the Sun. This puts it at, or beyond the star’s frost line, where volatile compounds like water, carbon dioxide, ammonia and methane condense into solid ice. As a result, the planet likely has a surface temperature in the region of -170oC, making it inhospitable to life as we know it – although if the planet has an atmosphere, its surface temperature could be higher.
This is the first time an exoplanet has been discovered using the radial velocity method. The most common method of detection is the transit method, monitoring the period dimming of a star’s brightness as seen from Earth to determine whether a planet might be orbiting it, but such is Barnard’s Star’s dimness, this has never really been and option.
Further observations are required to completely confirm the planet’s presence, but those involved in the study – including ESO – have a high degree of confidence it will be confirmed, and observations by a number of observatories around the globe are already underway.
After a very careful analysis, we are over 99 per cent confident that the planet is there, since this is the model that best fits our observations. However, we must remain cautious and collect more data to nail the case in the future … we’ll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet.
– Ignasi Ribas
Such is the proximity of Barnard’s Star to Earth, the new planet is potentially an excellent candidate for direct imaging using the next-generation instruments both on the ground and in space – such as with NASA’s James Webb Space Telescope (JWST), scheduled for launch in 2021) or Wide Field InfraRed Survey Telescope (WFIRST), which if not threatened with further cancellation, should be launched in the mid-2020s, and the European Space Agency’s Gaia mission.
‘Oumuamua Update
In my previous Space Sunday article, I wrote about our interstellar visitor, ‘Oumuamua (officially 1I/2017 U1), which was observed passing around the Sun a year ago, and the (unlikely) potential it is some form of extra-terrestrial probe.
On November 14th, 2018, NASA issued an update on the most recent findings from data obtained on the cigar-shaped object by the Spitzer infra-red telescope.
The new report, released via NASA’s Jet Propulsion Laboratory, indicates ‘Oumuamua is off-gassing volatiles, something those proposing the alien probe idea thought to be unlikely. This off-gassing likely imparted the odd tumbling motion exhibited by ‘Oumuamua . Spitzer’s observations also confirmed that the object is highly reflective – around 10 times more reflective than the comets that reside in our solar system—a surprising result, according to the paper’s authors.
Comets orbiting the Sun spend a good deal of their time gathering dust suspended in the interplanetary medium, covering them in a layer of “dirt”. As they approach the Sun, they undergo heating, causing volatiles – often frozen water – to start venting, “cleaning” parts of the comet’s surface and raising its reflectivity. As ‘Oumuamua, has been in the depths of interstellar space for millennia and far from any star system that could contain enough dust and material to refresh its surface, it is possible that the off-gassing confirmed by Spitzer exposed far more of its underlying ice. This, coupled with some of the icy volatiles it vented falling back onto its surface (again as can happen with solar system comets) may have resulted in the object’s higher than expected albedo.
Taken with other observations of ‘Oumuamua, the Spitzer data tends to further discount the idea that it is of artificial origin.
Continue reading “Space Sunday: exoplanets ‘Oumuamua and rockets”
Inara Pey: Living in a Modemworld 