The smallest extrasolar planet found around a star in the Main Sequence (i.e. not burned out or in an unstable phase) is a rocky planet near a red dwarf star, slightly larger than Mars. It is estimated that around one-third of all red dwarfs, which include more than three-quarters of all stars, have Earth-like planets. When do we find the first planet with life?
The newly discovered planet, KOI-961.03, periodically covers its star, periodically decreasing its brightness by a very small fraction. This is enough to get through the NASA's Kepler space telescope to be perceived.
The red dwarf star KOI-961 is very small compared to the sun, but it appears to have a solar system of at least three rocky planets: in addition to KOI-961.03, also the rock planets KOI-961.01 and KOI-961.02.
Out of breath at three miles altitude
The researchers combined Kepler's data with observations of the giant Keck Telescope on the five-kilometer-high volcano Mauna Kea on the Hawaiian island of Oahu. The very thin air at that enormous height makes work (and thinking) difficult for astronomers. They often write down in advance what they have to do before making the trip up (although there are of course options for teleworking nowadays).
Still, the Keck is on Mauna Kea for a reason. This site provides very good 'seeing' (clear image) because the summit already extends beyond half of the troposphere, the densest and most turbulent part of the atmosphere.
With the help of this ten-meter diameter telescope, they determined the exact size of the star. There is a fixed relationship between the size, luminosity and mass of a star. Because Kepler determines exactly how much the starlight is attenuated, the relative size of the planet disk is quite easy to calculate.
KOI-961.03 is the smallest observed planet with 0.57 times the diameter of the earth, approx. 8% bigger than Mars. The other planets KOI-961.02 and KOI-961.01 sit with resp. 0.73 and 0.78 times the size of the Earth, in between Mars and Earth.
Much smaller planet around pulsar discovered
Both KOI-961.02 and KOI-961.03 are smaller than any other exoplanet discovered so far around a star in the Main Sequence. A much smaller planet, about two percent of Earth's mass, the size of the Moon, has been discovered around a pulsar.
A pulsar, a dead star, collapsed into a sphere of neutrons 20 to 30 kilometers in diameter, with its extremely strong magnetic field and deadly X-rays does not provide a welcoming environment for life, but it is very easy to find planets around pulsars because they are very regular. give signals. Even a miniscule planet disrupts the pulsar clock measurably.
We have already described the first discovery of an extrasolar planet smaller than Earth. The following day this record was also shattered, with now the provisional smallness record. All these discoveries were made possible by Kepler.
Exo solar system similar to Jupiter galaxy
This newly discovered system is also the smallest solar system ever found. The planets are all less than four times farther from the star (1.5 million km) than Earth's moon. Similar to the distances from Jupiter's moons to the giant planet. In comparison, if the earth were that distance from the sun, the sun would take up a quarter of the sky, turn the earth into magma, and the earth would be torn apart by the tidal effects.
Although KOI 561 is much smaller than the sun, the living conditions on the trio of planets are far from pleasant, unless, for example, you are a silicon-based life form: even on the most distant, small planet there are hellish temperatures of 200 degrees. A 'year' lasts less than two days.
'Milky Way is teeming with small rocky planets'
Good news for the many of us who dream of a lovely exo Earth to ourselves. This is in addition to the ever-growing mountain of evidence that small rock planets are very common around red dwarfs, which make up about 80 percent of all the stars in the Milky Way. Only a few dozen of the 150,000 stars that Kepler is watching at the same time are as small as KOI-961. Because it is extremely coincidental for a planet to be just in front of a star, this discovery means that at least a third of these smallest red dwarfs have a planetary system, according to researchers. Team member John Johnson therefore compared them to cockroaches, of which you only see a few, but many more often hide.
Why haven't we found rocky planets in the habitable zone yet?
The further away a planet is from a star, the less likely it is that the planet will pass right in front of the star. Kepler also looks at the group of stars for a relatively short time. Suppose a planet has an orbit of a month or half a year, then there are no minimum two covers in the observation window and no hit is scored. The exoplanets discovered so far are almost all charred boulders for this reason. For example, at KOI-961, a planet must be three to six million kilometers from the star for life as we know it to be possible. Life forms on such a planet would see a huge, dull red sun and different constellations every night. Maybe we just have to be more patient until Kepler finds these planets.