Kepler object of interest facts for kids

A Kepler object of interest (KOI) is a star that the Kepler space telescope watched closely. Scientists thought these stars might have one or more planets passing in front of them. When a planet passes in front of its star, it's called a transit. This makes the star look a little dimmer for a short time.

KOIs are chosen from a huge list of 150,000 stars. The Kepler telescope looks for stars that dim regularly. This dimming could mean an unseen planet is passing between the star and Earth. But sometimes, other things can cause a star to dim. For example, another star in the background might be eclipsing it. Because of this, most KOIs are still not confirmed to have planets.

How KOIs Were Found

The first list of KOIs was shared with the public on June 15, 2010. It included 306 stars that might have exoplanets (planets outside our solar system). These were found from observations made between May and September 2009.

Scientists also found 400 more KOIs at that time. But they kept these secret for a while. This allowed the Kepler team to do more observations and check them first.

Later, on February 1, 2011, a second list was released. It had even more transit signals – 1235 of them around 997 stars! This new list used better ways to process the data.

Naming These Special Stars

Stars that Kepler watches and that might have planets are given a "KOI" name. This is followed by a number, like KOI 718.

If a star has more than one possible planet, each planet gets an extra number. For example, the first possible planet around KOI 718 is called KOI 718.01. The second is KOI 718.02, and so on.

Once scientists confirm that a KOI truly has a planet, the star gets a new name. It becomes "Kepler" followed by a number, like Kepler-219. The planets around it are then named with letters, such as Kepler-219b, Kepler-219c, and Kepler-219d.

What Kepler Data Tells Us

For all 150,000 stars Kepler watched, scientists estimated things like their surface temperature, radius (size), and mass (how much stuff they're made of). They got this information by measuring the stars' light before Kepler launched.

For KOIs, there's even more data about the dimming signals. This includes:

• How much the star dimmed (the depth of the signal).
• How long the dimming lasted (the duration).
• How often the dimming happened (the periodicity).

If the dimming is caused by a planet, this data helps scientists figure out:

• The planet's size compared to its star.
• How far the planet is from its star.
• The planet's orbital period (how long it takes to go around its star).

By combining this with the star's estimated properties, scientists can guess the planet's actual size, its distance from the star, and its temperature.

Confirming Planet Candidates

It's very important to check if a KOI really has a planet. Sometimes, the dimming could be a "false positive" – meaning it's not a planet at all.

One good way to confirm a planet is to measure the star's "wobble." A planet's gravity can make its star wobble slightly. This is called radial velocity measurement.

For many KOIs, this wobble is too small to measure. So, scientists use other methods. They use powerful ground-based telescopes with special tools like speckle imaging or adaptive optics. These tools help them see if there are other stars in the background causing the dimming. These checks can reduce the chance of a false alarm to less than 0.01%!

Scientists can also take spectra (light fingerprints) of the KOIs. This helps them see if the star is actually part of a binary system (two stars orbiting each other).

Interesting KOIs

Stars with Confirmed Planets

As of August 2016, the Kepler mission had found 2329 confirmed planets orbiting 1647 stars. They also had 4696 planet candidates that still needed more checking.

Planets Found Before Kepler

Some planets were already known before Kepler started its mission. Kepler re-observed three of these stars: GSC 03549-02811, HAT-P-7, and HAT-P-11. These stars are now called Kepler-1, Kepler-2, and Kepler-3.

Planets Confirmed by the Kepler Team

The Kepler team first spotted signals from these eight stars that suggested planets were orbiting them. They later confirmed these planets: Kepler-1658, KOI-5, Kepler-4, Kepler-5, Kepler-6, Kepler-7, Kepler-8, Kepler-9, Kepler-10, and Kepler-11.

• Kepler-9 has 3 confirmed planets.
• Kepler-11 has 6 confirmed planets!

Planets Confirmed by Other Groups

Scientists from other research groups also used Kepler's public data. They confirmed one system, Kepler-40, has a planet.

Stars with Unconfirmed Planets

Kepler-20 (also known as KOI-70) shows signs of at least four planets. One of them, KOI-70.04, might be the smallest exoplanet found around a main-sequence star. It's only about 0.6 times the size of Earth.

In 2011, six transit signals were found that looked like "Earth-like" planets (less than twice Earth's size) located in the "habitable zone" of their stars. The habitable zone is the area around a star where it's not too hot and not too cold for liquid water to exist, which is important for life. These candidates were: KOI 456.04, KOI 1026.01, KOI 854.01, KOI 701.03, KOI 326.01, and KOI 70.03. However, later studies showed that KOI 326.01 is actually much bigger and hotter than first thought. For now, KOI 456.04 is the most promising "Earth-like" candidate in the habitable zone around a star like our Sun. It orbits the star Kepler-160.

Other Interesting Discoveries

Some KOIs have objects passing in front of them that are actually hotter than the stars themselves! This means the smaller objects are white dwarfs. White dwarfs are tiny, super-dense stars that are the leftover cores of dead stars. These include KOI 74, KOI 81, and KOI 959.

KOI 54 is a system with two large stars called A-class stars. They orbit each other in a very stretched-out path. When they get closest, their gravity pulls on each other, making them brighten. This also causes one or both stars to pulse, which is very rare!

KOI 126 is a system with three stars. Two small stars orbit each other very closely, and then both of them orbit a larger star. All three stars eclipse each other. This allows scientists to measure their sizes and masses very precisely.

KIC 8462852 is a star with a very mysterious dimming pattern. Scientists are not sure what causes it. One idea is that it's dust from broken-up comets. Some astronomers are even studying it for signs of alien life! This is because the way its light changes could look like a huge alien structure, like a Dyson sphere, if seen by Kepler.