A Very Wobbly Planet Found by Kepler
Kepler was designed to detect ecoplanets by noticing the dips in brightness caused when these worlds transit, or cross in front of, their parent stars. Normally these transits occur in a regular pattern, but Kepler-413b behaved strangely.
Imagine living on a planet with seasons so erratic you would
hardly know whether to wear Bermuda shorts or a heavy overcoat. That is the
situation on a weird, wobbly world found by Kepler space telescope.
The planet, designated Kepler-413b, precesses, or wobbles, wildly
on its spin axis, much like a child's top. The tilt of the planet's spin axis
can vary by as much as 30 degrees over 11 years, leading to rapid and erratic
changes in seasons. In contrast, Earth's rotational precession is 23.5 degrees
over 26,000 years. Researchers are amazed that this far-off planet is
precessing on a human timescale.
Kepler 413-b is located 2,300 light-years away in the
constellation Cygnus. It circles a close pair of orange and red dwarf stars
every 66 days. The planet's orbit around the binary stars appears to wobble,
too, because the plane of its orbit is tilted 2.5 degrees with respect to the
plane of the star pair's orbit. As seen from Earth, the wobbling orbit moves up
and down continuously.
Kepler finds planets by noticing the dimming of a star or stars
when a planet transits, or travels in front of them. Normally, planets transit
like clockwork. Astronomers using Kepler discovered the wobbling when they
found an unusual pattern of transiting for Kepler-413b.
Looking at the Kepler data over the course of 1,500 days,
scientists saw three transits in the first 180 days -- one transit every 66
days -- then had 800 days with no
transits at all. After that, they saw five more transits in a row. The next
transit visible from Earth's point of view is not predicted to occur until
2020. This is because the orbit moves up and down, a result of the wobbling, in
such a great degree that it sometimes does not transit the stars as viewed from
Earth.
Astronomers are still trying to explain why this planet is out of alignment
with its stars. There could be other planetary bodies in the system that tilted
the orbit. Or, it could be that a third star nearby that is a visual companion
may actually be gravitationally bound to the system and exerting an influence.
Even with its changing seasons, Kepler-413b is too warm for life
as we know it. Because it orbits so close to the stars, its temperatures are
too high for liquid water to exist, making it inhabitable. It also is a super Neptune -- a giant gas planet with a mass about 65 times
that of Earth -- so there is no surface on which to stand.
