Kepler Discovers ‘Wobbly Planet’ Kepler-413b

Kepler Space Telescope discovers wobbly planet Kepler413b

Astronomers have recently discovered the existence of a “wobbly planet,” which precesses considerably on its spin axis. Akin to a child’s top, the planet’s spin axis can vary hugely – by as much as 30 degrees over a period of more than 11 years – culminating in diverse changes to the seasons. For comparison, the Earth’s spin axis can change by 23.5 degrees over a timeframe of 26,000 years. Regardless of the rapid and unpredictable seasonal fluctuations that are triggered by the planet’s wobble, the super-Neptune orbits much too close to its host stars to be considered “habitable.” Indeed, Kepler-413b lies outside of its habitable zone – defined as the region at which temperatures would be amenable to sustaining liquid water and, perhaps, biological life.

Kepler-413b’s Wobble Determined by Unusual Transit

The planet in question is called Kepler-413b, and is located some 2,300 light-years from Earth in the constellation Cygnus – a constellation that derives itsĀ name from the Greek word for swan. Every 66 days, Kepler-413b orbits a red dwarf star and an orange dwarf star, paired close to one another. Aside from

26,000 year cycle of precession with current north pole at Polaris
26,000-year cycle of precession for Earth, with current north pole at Polaris. The Earth slowly wobbles, describing a circle in the sky.

this, the unusual planet demonstrates a wobbly orbit, bobbing up and down, continuously; this is because the plane in which the planet orbits is titled at an angle of 2.5 degrees, relative to the plane of its host stars’ orbits.

Kepler-413b’s peculiar motion was detected by the Kepler Space Telescope, which locates planets by perceiving the dimming that occurs when a particular planet transits in front of its host star. Ordinarily, most planets that transit their host stars do so in a regular pattern; however, astronomers were puzzled to find that Kepler-413b did not adhere to such a pattern and, instead, observed changes in the time periods between each transit. The study’s lead investigator Veselin Kostov, based at the Space Telescope Science Institute and John Hopkins University, discussed his team’s findings in a recent press release:

“What we see in the Kepler data over 1,500 days is three transits in the first 180 days (one transit every 66 days), then we had 800 days with no transits at all… After that, we saw five more transits in a row.”

Astronomers Unsure as to Cause of Strange Orbit

Kostov’s group came to the conclusion that the different time periods, between each transit, resulted from the planet wobbling so radically that it sometimes does not transit in front of its host star, when viewed from the position of the Earth. In light of this evidence, the researchers estimate that Kepler-413b’s next transit will not be visible from Earth’s viewpoint until 2020.

Illustration showing unusual orbit of Kepler 413b around dwarf stars
Illustration showing the unusual orbit of Kepler-413b around its host dwarf stars. Image credit: NASA, ESA, and A. Feild (STScI).

In fathoming the reason for this phenomenon, astronomers have formulated a series of theories. Chiefly, the group suspect there could be other planetary bodies present within the system, causing Kepler-413b to demonstrate a tilted orbit. However, it is also possible that a third, nearby star that is a visual companion may be bound to the system and having an impact on the planet’s orbit.

Peter McCullough, of the Space Telescope Science Institute and John Hopkins University, conjectures there to be other planets out there that are similar to Kepler-413b; however, researchers have simply been unable to detect these planets, due to their atypical orbits. McCullough elaborates upon this point: “…that’s one of the things that Veselin is researching: Is there a silent majority of things that we’re not seeing?”

The results of the study were published in the Astrophysical Journal, and the paper was entitled Kepler-413b: a Slightly Misaligned, Neptune-Size Transiting Circumbinary Planet.

By James Fenner


Astrophysical Journal
NASA Press Release
Los Angeles Times
National Geographic

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