When a planet such as K2-33b passes in front of its host star, it blocks
some of the star's light. Observing this periodic dimming, called a
transit, from continual monitoring of a star's brightness, allows
astronomers to detect planets outside our solar system with a high
degree of certainty. This Neptune-sized planet orbits a star that is
between 5 and 10 million years old. In addition to the planet, the star
hosts a disk of planetary debris, seen as a bright ring encircling the
star. Youtube
K2-33b, shown in this illustration, is one of the
youngest exoplanets detected to date. It makes a complete orbit around
its star in about five days.
Credits: NASA/JPL-Caltech.
Credits: NASA/JPL-Caltech.
This image shows the K2-33 system, and its planet
K2-33b, compared to our own solar system. The planet has a five-day
orbit, whereas Mercury orbits our sun in 88 days. The planet is also
nearly 10 times closer to its star than Mercury is to the sun. Credits: NASA/JPL-Caltech
Astronomers have discovered the youngest fully formed exoplanet ever
detected. The discovery was made using NASA's Kepler Space Telescope and
its extended K2 mission, as well as the W. M. Keck Observatory on Mauna
Kea, Hawaii. Exoplanets are planets that orbit stars beyond our sun.
The newfound planet, K2-33b, is a bit larger than Neptune and whips
tightly around its star every five days. It is only 5 to 10 million
years old, making it one of a very few newborn planets found to date.
"Our Earth is roughly 4.5 billion years old," said Trevor David of
Caltech in Pasadena, lead author of a new study published online June
20, 2016, in the journal Nature. "By comparison, the planet K2-33b is
very young. You might think of it as an infant." David is a graduate
student working with astronomer Lynne Hillenbrand, also of Caltech.
Planet formation is a complex and tumultuous process that remains
shrouded in mystery. Astronomers have discovered and confirmed roughly
3,000 exoplanets so far; however, nearly all of them are hosted by
middle-aged stars, with ages of a billion years or more. For
astronomers, attempting to understand the life cycles of planetary
systems using existing examples is like trying to learn how people grow
from babies to children to teenagers, by only studying adults.
"The newborn planet will help us better understand how planets form,
which is important for understanding the processes that led to the
formation of Earth," said co-author Erik Petigura of Caltech.
The first signals of the planet's existence were measured by K2. The
telescope's camera detected a periodic dimming of the light emitted by
the planet's host star, a sign that an orbiting planet could be
regularly passing in front of the star and blocking the light. Data from
the Keck Observatory validated that the dimming was indeed caused by a
planet, and also helped confirm its youthful age.
Infrared measurements from NASA's Spitzer Space Telescope showed that
the system's star is surrounded by a thin disk of planetary debris,
indicating that its planet-formation phase is wrapping up. Planets form
out of thick disks of gas and dust, called protoplanetary disks, that
surround young stars.
"Initially, this material may obscure any forming planets, but after a
few million years, the dust starts to dissipate," said co-author Anne
Marie Cody, a NASA Postdoctoral Program fellow at NASA's Ames Research
Center in California's Silicon Valley. "It is during this time window
that we can begin to detect the signatures of youthful planets with
K2."
A surprising feature in the discovery of K2-33b is how close the
newborn planet lies to its star. The planet is nearly 10 times closer to
its star than Mercury is to our sun, making it hot. While numerous
older exoplanets have been found orbiting very tightly to their stars,
astronomers have long struggled to understand how more massive planets
like this one wind up in such small orbits. Some theories propose that
it takes hundreds of millions of years to bring a planet from a more
distant orbit into a close one -- and therefore cannot explain K2-33b,
which is quite a bit younger.
The science team says there are two main theories that may explain
how K2-33b wound up so close to its star. It could have migrated there
in a process called disk migration that takes hundreds of thousands of
years. Or, the planet could have formed "in situ" -- right where it is.
The discovery of K2-33b therefore gives theorists a new data point to
ponder.
"After the first discoveries of massive exoplanets on close orbits
about 20 years ago, it was immediately suggested that they could
absolutely not have formed there, but in the past several years, some
momentum has grown for in situ formation theories, so the idea is not as
wild as it once seemed," said David.
"The question we are answering is: Did those planets take a long time
to get into those hot orbits, or could they have been there from a very
early stage? We are saying, at least in this one case, that they can
indeed be there at a very early stage," he said.
Ames manages the Kepler and K2 missions for NASA's Science Mission
Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California,
managed Kepler mission development. Ball Aerospace & Technologies
Corporation operates the flight system with support from the Laboratory
for Atmospheric and Space Physics at the University of Colorado at
Boulder.
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov
Michele Johnson
Ames Research Center, Moffett Field, Calif.
650-604-6982
michele.johnson@nasa.gov
Felicia Chou
NASA Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov
Written by Whitney Clavin
Editor: Tony Greicius
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov
Michele Johnson
Ames Research Center, Moffett Field, Calif.
650-604-6982
michele.johnson@nasa.gov
Felicia Chou
NASA Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov
Written by Whitney Clavin
Editor: Tony Greicius
Source: NASA/Kepler and K2