Star with seven red-hot planets discovered in data from retired space telescope

Five years after the active life of the Kepler space telescope came to an end, scientists have discovered a new solar system with no fewer than seven planets in the enormous amount of data collected by the telescope.

The planets in question orbit Kepler-385: a Sun-like star that is 10 percent larger and 5 percent warmer than our parent star. The inner two planets are slightly larger than Earth and probably rocky. They are also believed to possess a thin atmosphere. The outer five planets are about twice larger than our home planet and are likely shrouded in a thick atmosphere.

The system is special for several reasons. To date, we are only aware of a few solar systems with more than six verified (see box) planets. What is also striking is that this system consists of planets that are all glowing hot. “Kepler-385 is the first discovered planetary system that hosts seven hot planets,” said researcher Jack Lissauer.

Planet hunter Kepler was operational between 2009 and 2018 and detected planets using the so-called transit method. Basically, the space telescope stares at stars for a long time, hoping to witness their brightness diminishing at regular intervals. Such dips in brightness can then hint at the presence of a planet that occasionally passes between its parent star and Kepler, temporarily blocking some of the star’s light. Kepler has discovered thousands of candidate planets in this way. These are planets whose existence is plausible, but not yet proven, based on Kepler observations. Follow-up observations (often using other telescopes) are needed to verify its existence and turn a planet candidate into a planet.

Glowing hot
Kepler studied Kepler-385 for a long time and found decreases in brightness that hinted at the presence of planets. The existence of some of those planets was already confirmed in 2014. But a reanalysis of the old Kepler data now allows researchers to also promote the remaining candidate planets around Kepler-385 to planet status. And that brings the total number of planets discovered around this star to seven! The researchers can also characterize these planets reasonably well and, for example, say more about their size, nature (rocky or not) and atmosphere. In addition, we know that the planets are very close to their star and are therefore bathed in starlight. The result is obvious: the planets are scorching hot.

Important information
“It new research shows that a lot of information can still be extracted from the Kepler mission, even though it has already ended,” says researcher Jason Steffen. “By examining these distant planetary systems, we can get a better sense of our own history and how it differs from the histories of other systems.”

About the research
The discovery that seven planets orbit Kepler-385 is just one of the highlights of a new study, in which scientists re-analyzed the data collected by Kepler between 2009 and 2018. The goal was not only to use that analysis to confirm the existence of a number of candidate planets; the researchers also wanted to characterize the planets discovered by Kepler more precisely. “Now that we’ve had some time to analyze the data, we can refine our estimates of some properties of planets in different systems, such as their orbital periods and sizes,” Steffen explains. “This is the ultimate catalog of planets discovered during the Kepler mission.” This ‘catalogue’ contains almost 4400 (candidate) planets. Some of these planets are not alone, but are accompanied by one or more planets as they orbit the parent star: more than 700 of these multiplanetary systems can be found in the new catalogue. “We have compiled the most accurate list of planet candidates and their properties ever discovered by Kepler,” Lissauer concludes.

The new catalog is also made possible by other observatories. For example, the researchers used Gaia: a satellite that can very accurately determine the distance, position and movements of stars and also monitor changes in the brightness of those stars. This data not only provides much more information about the stars in question, but is also relevant to our understanding of any planets orbiting them. For example, researchers can use the Gaia data to accurately determine the orbital period of a planet. An analysis of these circulation times also results in a remarkable discovery. Namely, planets that are part of a system containing several planets generally have a more circular orbit than planets that orbit a parent star alone or with one companion.

Of course, the catalog is not just a finished product; researchers hope it is the prelude to more. Namely a better understanding of other planetary systems and therefore also a better picture of how special ours – with life in it – may or may not be.