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Caltech, NASA Discover Youngest Exoplanet Orbiting Young Star

The complex and turbulent process of how planets formed is still quite a mystery. So far, over 3,000 exoplanets have been located by astronomers. Exoplanets are planets that orbit the stars rather than the Earth’s Sun. most of these are middle-aged – extending to over a billion years.

K2-33 b, shown in this illustration, is one of the youngest exoplanets detected to date and makes a complete orbit around its star in about five days. These two characteristics combined provide exciting new directions for planet-formation theories. K2-33 b could have formed on a farther out orbit and quickly migrated inward. Alternatively, it could have formed in situ, or in place. (Photo credit: NASA/JPL-Caltech)

A team of researchers led by Caltech have located the youngest totally-formed exoplanet ever discovered. The new planet referred to as K2-33b is about 5 to 10 million years old, and is considered to still be in its infancy.

During NASA's K2 mission, its Kepler space telescope measured the first signals of the planet's presence. The telescope identified a intermittent dimming of the light produced by the host star - K2-33 - of the planet, which points to the existence of an orbiting planet.

The existence of the planet was further validated by the observations conducted from the W.M. Keck Observatory in Hawaii. The dimming of light was definitely caused by a planet, which was later christened K2-33b. A paper specifying the findings was published in online issue of the journal Nature.

At 4.5 billion years old, the Earth is a middle-aged planet—about 45 in human-years. By comparison, the planet K2-33b would be an infant of only a few weeks old.

Trevor David, Graduate Student, Caltech

"This discovery is a remarkable milestone in exoplanet science," says Erik Petigura, a postdoctoral scholar in planetary science and a coauthor on the paper. "The newborn planet K2-33b will help us understand how planets form, which is important for understanding the processes that led to the formation of the earth and eventually the origin of life."

During the formation of stars, they are surrounded by thick areas of dust and gas referred to as protoplanetary disks, from which planets form. The disk mostly dissipates by the time a star in its infancy turns a few million years old, and planet formation is almost complete.

The star orbited by K2-33b still has a bit of disk material left. This was revealed from the observations conducted using NASA's Spitzer space telescope, and it indicates that the disk is in its last stages of dissipation.

K2-33b was formerly spotted as a potential planet candidate during a survey of stars performed during the K2 mission, which was the prolonged mission phase of the Kepler Space Telescope.

Astronomers know that star formation has just completed in this region, called Upper Scorpius, and roughly a quarter of the stars still have bright protoplanetary disks. The remainder of stars in the region do not have such disks, so we reasoned that planet formation must be nearly complete for these stars, and that there would be a good chance of finding young exoplanets around them.

Trevor David, Graduate Student, Caltech

K2-33b, like several other exoplanets, was identified due to the intermittent dimming in the light of the central star as the planet passed before it. The team could establish the orbital period and size of the planet by analyzing the frequency of dips in the light of the star and measuring by the amount of light dimmed. According to Petigura, K2-33b is "a remarkable world".

The exoplanet, which is approximately 50% larger than Neptune and nearly six times the size of Earth, is able to fully orbit its host star in approximately five days. This indicates that the exoplanet is 20 times nearer to its star than the Earth is to the Sun.

K2-33b is a large planet similar to the gas giants in the Earth’s solar system. In the Earth’s solar system, these massive planets are all at great distances from the Sun. The fact is that the closeness of the massive planet K2-33b to its star is not highly unusual for planets in the Earth’s galaxy, where several of them are quite "close in," frequently orbiting around their parent star within weeks or even days. The reason for this is that massive planets sometimes are formed far from their host star and tend to move closer over time.

The position of K2-33b is already quite close to its host star at this early age, which indicates that if any migration happened, it was fast.

On the other hand, the planet could be confirmation against the migration hypothesis, signifying that massive planets can in reality form at close proximity to their stars.

Discovering and studying K2-33b required using several of the most powerful astronomical instruments available, both in space and on Earth.

Sasha Hinkley, Senior Lecturer, Exeter University

As a NASA Sagan Postdoctoral Fellow at Caltech, Hinkley collected data from the Keck telescope which was later applied in the verification of the planet’s existence.

K2-33b is completely formed, but there is still a chance that it may evolve in the future.
The subsequent step is to calculate the mass of the planet and establish its density. These measurements will assist in understanding the fate of the planet in the years ahead -whether it will remain around the same size or whether it will cool down and reduce in size.

The results are illustrated in a paper titled, "A Neptune-sized transiting planet closely orbiting a 5–10 million-year-old star." The research was supported by a National Science Foundation Graduate Research Fellowship. A portion of the data was funded by NASA. Professor Lynne Hillenbrand, staff scientist David Ciardi, and senior faculty associate in astronomy Charles Beichman were supplementary Caltech coauthors on this paper.

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