It’s startling to believe sometimes, that it’s been nearly 20 years since the first discovery of planets outside our solar system. New exoplanets are still being discovered constantly, with nearly 500 confirmed detections so far. The tools in the planet hunters’ arsenal are becoming ever more sophisticated, and every now and again an impressive discovery is made. A discovery like the planetary system around HD 10180 — the first system of planets to be detected which is sufficiently populous to rival our own!
HD 10180 is a sun-like star in our part of the galactic suburbs, a mere 127 light years away. A G1V class star, it’s a little bit more massive than the Sun, and so also a little bit hotter and a little bit more luminous. From an astrobiological perspective, that makes it a prime target to look for life-bearing planets. The exciting part is that HD 101080 appears to have at least 5 exoplanets. In fact, it may possibly have as many as 7 worlds in tow around it! Wow!
Christophe Lovis and his team of planet hunters reported this discovery recently. Their work used ESO’s HARPS (High Accuracy Radial velocity Planet Searcher) instrument to take 190 individual measurements to look for the tiny gravitational tugs that planets would cause on a star. HARPS is one of the most accurate radial velocity spectrographs in the world. Of the planets they’ve found, the innermost 5 are approximately Neptune-sized, and their detections are accurate to well under 1% error. That’s a pretty solid set of detections! They also picked up a couple of weaker signals in their data. In the world of exoplanets, weaker signals either come from smaller or more distant planets. Of these two further signals, one may be due to a Saturn-sized planet at 3.4 AU from the central star, with a probability of just 0.6% that this is a false detection. The other, with a slightly larger 1.4% probability of a false detection, is a nearly Earth-sized planet at 0.02 AU. With a mass as low as 1.4 Earth masses, this could be the smallest exoplanet ever detected. Interestingly, all of these planets are in tidy, circular orbits, showing none of the wild eccentricity seen in other systems.
With 5 neptune-like planets squeezed into a space the size of Mars’ orbit, HD 101080 is a busy system. If those planets also have moons (and judging by our own solar system, there’s good reason to believe that they could) then HD 101080 could be an all round fascinating place. The possiblity of any kind of life in this system is encouraged by the age of the central star. At 7.6 billion years old, HD 10180 is a lot older then the Sun, so complex chemistry in the system has had plenty of time to occur. The star is also 20% more metal rich than the Sun, which also ties in conveniently with the number of observed planets. The most massive planetary systems, as you might expect, are found around stars with more heavy elements from which to construct them.
Following the previous record holding exoplanet system of 5 planets around 55 Cancri, it seems our telescopes are fast becoming accurate enough to detect ever more complete planetary systems. Excitingly, I’d expect quite a few more systems like this one to be discovered in years to come…