A planetary system has been discovered.
In KOI-351, the orbits of all seven planets fit together in a space smaller than the Earth’s path from the Sun — twenty times more compact than our system! And the discoverers of the seventh exoplanet warn that, perhaps, this is not the last find.
As you may recall, astronomy-loving volunteers with we noticed slight fluctuations in the luminosity of the star KIC 4862625, located 5 thousand light — years away in the constellation Cygnus, and found there the first known planet with a system of four stars at once. Since then, the efforts of the community have been regularly rewarded with discoveries, the latest series of which we would like to introduce you to.
Now imagine this whole collection (without Neptune) inside the Earth’s orbit. Twenty times more compact than in our system! (Illustration by Shutterstock.)
Joseph Schmitt of Yale University and amateur astronomer Daryll Lacourse report the discovery of 14 new planet candidates found in the Kepler archives by the transit method. Moreover, none of them was marked by professionals as “an object of possibly planetary nature”, and the special search algorithm Kepler Transit Planet Search, designed to automate such work, missed five of them. Why?
Fluctuations in luminosity make it relatively easy to search for “automatic” exoplanets only in the system of one star. Where there are two, three, or four stars, the oscillations can be much more complex, so it can be difficult to distinguish planets from them (at least for algorithms). Amateurs-due to their large number — are able to manually process such a large number of materials that professionals can not often dig through, and their ability to analyze in non-trivial conditions is obviously higher than that of algorithmic search.
So, what kind of exoplanets were discovered this time: eight are in the habitable zone of their stars, and two “live” in systems with already known planets. Especially interesting in this sense is the discovery of one of them: before that, six planets were found in KOI-351, so now we can talk about the first system of seven planets (recorded by Kepler). So far, the candidate for the seven-planet system (HD 10180) has been declared only on the basis of the HARPS spectrograph, which uses a fundamentally different method for detecting exoplanets. In addition, the planet hunters note, only six HARPS bodies have confirmed status, while in seven KOI-351 planets, the authors of the work in question are “firmly confident”.
At first glance, this” at least seven-planet ” system is similar to our own. The star there is slightly larger than the Sun, and has a surface temperature of 6,000 K. The first five planets in it are “super-earths” and “mini-neptunes”. And a little further away is a pair of gas giants. But the similarity is remote and deceptive: all seven candidates rotate no further than one astronomical unit from their star (0.98 au), and the closest is 0.075 au (11 million km)from the sun! In other words, they are trapped in a region that we would fit between the Sun and the Earth, and the seventh body is twenty times closer to the star than Uranus (the seventh planet of the Sun). Individual planets — two bodies the size of the Earth-have orbits that are less than 2 million km apart, meaning that in the night sky, each of them shines as brightly as our Moon.
A newly discovered planet with a radius of 2.8 earth’s (mini-Neptune), has a 125-day rotation period; it is the fifth in a row from the sun; so far, it has been difficult to find it by transits both in front of the planet and behind it.
One more time: this is the first exoplanet system to be so densely populated. In the mentioned HD 10180, the most distant planet is 3.5 au away from its star, that is, several times farther than in KOI-351. Think about it: the distance from the nearest to the farthest of the orbits of all seven planets is less than 140 million km, on average about 20 million km between the “neighbors”! Our average distance between orbits is measured in hundreds of millions of kilometers, and even the closest neighbors are separated at best by 40-50 million km.
It may seem that the presence of two gas giants next to five planets smaller than Neptune should eventually destabilize the orbits of the latter. However, the attempts of the “planethunters “to simulate the evolution of such a system showed that, despite the terrible” density”, the neighbors in the communal apartment do not interfere too much with each other, and over the next 100 million years, the system looks stable.
With all these ideal conditions for interplanetary travel, it is unlikely that anyone will be able to take advantage of them. Neither on the open candidate planets, nor even on their satellites, there is no smell of habitability yet: they are too close to the sun to support earth-type life in the absence of the strongest clouds. However, as the authors of the study note, KOI-351 will still require increased attention, since only “near” exoplanets are first found in multi-planetary formations of this type. And hypothetical (not yet discovered) bodies may well be further away from the sun, thus falling into the habitable zone.
In our time, the illustration of a particular system is often outdated even before its creation: there are only five planets in this diagram, although now there are seven. However, the internal and external borders have not changed. For comparison, the Earth (blue), Venusian (orange) and Mercurian (red) orbits are shown.
Among the other newly discovered planets, there are eight bodies that formally lie in the habitable zones, but only one or two are similar in size to “super–earths”. The rest are classified as “mini-neptunes”, where even being in the habitable zone can only contribute to the development of life on large moons such as our Titan or Europa.