The planets seem as massive as the Earth, but they have to do without the parent star.

Astronomers discovered the four planets in data collected in 2016 by the Kepler space telescope. telescope – retired now Then he examined the heart of the Milky Way, hoping to find new exoplanets. The so-called microgravity technology was used for this.

microgravity lens
In a microgravitational lens, researchers cleverly use the light coming from bright stars far from Earth. When another star passes in front of such a bright star, the forward star’s gravity causes the light from the distant star to be bent and amplified. The star in the foreground acts as a kind of lens. This appears to temporarily increase the brightness of that distant star for several hours or days. If you look at the light curve of this star, you’ll see a significant peak arising from that “lens” in the foreground. When a planet orbits that star in the foreground, it also acts as a lens, temporarily amplifying the light from the star even further. This results in a second – more modest – peak in the light curve (see image below).

Photo: ESA.

Four new signs
The researchers have now recovered 27 of these tiny lens signals in the Kepler data. 23 of these have already been observed in data from ground-based telescopes that simultaneously surveyed this part of the universe. But the four shorter signs are new to us and seem to come from planets the same mass as Earth.

orphan planets
It should also be noted that the influence of these planets on the light curves of distant stars does not correlate with the influence of their parent star. It indicates that these are called orphan planets. These are planets wandering singly through space without a star. Such orphan planets are believed to have once appeared around a parent star, but were later expelled from their solar systems by interactions with other, more massive planets.

Special
Kepler’s discovery of lonely planets through a fine lens is very special. Not least because Kepler wasn’t actually made to search for exoplanets using microgravity technology. The telescope for detecting exoplanets was developed on the basis of a decrease in the brightness of the parent star, caused by the movement of the exoplanets in front of this parent star. But as Kepler got older and began to struggle with the problems that made this approach difficult, the researchers changed tack and began looking for subtle lens cues. “These signals are very hard to find,” researcher Ian MacDonald notes. “For our observations, an old telescope sick with blurry vision was pointed at one of the busiest parts of the universe, where there are thousands of stars whose brightness actually varies anyway. There are also thousands of asteroids moving in our field of view. In this cacophony we try to notice the slight increases. in the brightness caused by the planets. And we have only one chance to detect such a signal – before it disappears again.”

The fact that Kepler has now spotted four orphaned planets in the heart of our galaxy in this way, according to researcher Eamonn Kerns, cautiously suggests the existence of “a group of single planets with a mass similar to that on Earth.” Future missions – like NASA’s mission بعثة Nancy Grace Roman Space Telescope And perhaps also ESA’s Euclid – may confirm the existence of such a population and also provide further insight into the life story of these orphaned planets.