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An Exo-Venus in the Solar Neighborhood

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exo-Venus
Artist’s impression of a Venus-like exoplanet orbiting close to its host star. [CfA/Dana Berry]
Venus vs. Earth

A size comparison of Venus and Earth. Though they are nearly the same size and density, these two planets evolved very differently. [NASA]

Earth is great place for life — but Venus definitely isn’t. Both planets have similar masses and densities. So why did one evolve to support life, while the other turned into a barren and inhospitable hothouse? This is a question we might be able to answer if we can gather observations of other planets similar to Earth and Venus. The recent discovery of an exo-Venus in our solar neighborhood brings us one step closer to this goal!

A New Neighbor

A team of scientists led by Isabel Angelo (SETI Institute, NASA Ames Research Center, and UC Berkeley) has announced the discovery of Kepler-1649b, an exoplanet transiting a star located just 219 light-years away from us. Kepler-1649b is unique in being roughly the same size as Earth and Venus and also receiving a similar amount of starlight as Venus does from our Sun.

Light curve

Phase-folded light curve showing the transit of Kepler-1649b. [Angelo et al. 2017]

Angelo and collaborators conducted follow-up observations after Kepler’s detection of 1649b to verify its planetary nature and pin down its properties. They found that Kepler-1649b has a radius of 1.08 times that of Earth, and it receives an incident flux of 2.3 times Earth’s — which is very similar to the incident flux received by Venus. Kepler-1649b orbits a star that’s only a quarter of our Sun’s radius, however, and it therefore orbits significantly closer to its star in order to receive the same flux, circling its host once every 8.7 days.

Differences Due to a Small Host

It’s worth identifying how this planet might differ from Venus. The authors suggest a few key factors:

  1. Kepler-1649b may be more prone to effects of host-star variability. M-dwarf stars like this one are typically more magnetically active than our Sun, and Kepler-1649b is orbiting very close to its star.
  2. Kepler-1649b receives comparatively low-energy radiation, compared to Venus. This is because its cooler host emits more light at lower frequencies than the Sun.
  3. Kepler-1649b may be subject to larger tidal effects from its host star. Because it orbits so close in, it might experience tidal heating, synchronous rotation, and tidal locking — all of which can influence its seasons and geologic activity.

Target for the Future

Kepler-1649b

The colored contours show the most likely radius and incident flux measured for Kepler-1649b. Earth, Venus, Mars, and several other exoplanets are plotted for comparison. [Angelo et al. 2017]

In spite of these differences, Kepler-1649b still qualifies as the most similar exoplanet we’ve found to Venus in terms of its size and incident radiation. This marks our first opportunity to study such a target to understand how it differs from Earth-like planets and what conditions might lead to habitability on a planet.

We will be able to gain more information on Kepler-1649b with upcoming missions. The Transiting Exoplanet Survey Satellite (TESS) will observe more transits, and Gaia’s improved-accuracy distance measurements should also improve our measurements of the star’s and planet’s properties. What’s more, Kepler-1649b will make an excellent target for the James Webb Space Telescope (launching in 2018) to examine in the hopes of learning about its atmosphere.

Citation

Isabel Angelo et al 2017 AJ 153 162. doi:10.3847/1538-3881/aa615f