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Have scientists found our first
exomoon? Looks like they still

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need more observations to be a
hundred percent sure. The moons

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in our solar system are very
diverse, some with liquid water,

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some that are potentially
habitable, so being able to

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observe moons in different solar
systems would give us a whole

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new treasure trove of
interesting worlds to study. The

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team of astronomers from
Columbia University sifted

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through data from 284 Kepler
measurements of transiting

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exoplanets. A transit happens
when a planet passes directly

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between us and its star and
blocks out a small portion of

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the star’s light, which produces
a dip in the amount of light

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coming from that star over time,
called a light curve. Out of the

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284 planets the team looked at.
they found one planet with an

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extra wobble in its light curve
that might be a moon. The team

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only had Kepler data from three
transits of this exoplanet, so

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they sent a proposal to the
Hubble Space Telescope to

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capture more data of this
possible exomoon. Hubble can

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measure light curves much more
precisely than Kepler, so Hubble

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can more definitively confirm or
debunk the existence of this

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exomoon once it gets multiple
transits. So far, the team of

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astronomers has collected Hubble
observations of one transit of

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exoplanet Kepler-1625b. The
planet transited across the face

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of its star for 19 hours, as
expected. Then, about three and

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a half hours later, a second
smaller dip in the light curve

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started. That right there is
intriguing evidence of an

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exomoon. The Hubble observation
of this star unfortunately

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concluded before the possible
moon finished its transit, so

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Hubble hasn’t yet observed a
full transit. This

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light curve appears like it
shows an exomoon, but we can’t

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say it’s a definitive detection
until Hubble observes at least

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one more transit. If this is
actually a moon, what do we know

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about it? The planet
Kepler-1625b is likely several

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times the mass of Jupiter. Its
possible moon appears to be

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about the mass and radius of
Neptune. Neptune-sized moons are

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obviously not something that
exist in our own solar system,

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and we’re not sure exactly how
such a moon would form. Finding

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planets and moons so different
from the ones in our own solar

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system gives us a lot more
knowledge of the many diverse

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ways planetary systems can
exist. In the near future,

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scientists hope to use the
Hubble Space Telescope to try to

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confirm the discovery of this
exomoon, and they’ll use Hubble

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for follow-up observations of
other planetary systems

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discovered by observatories like
Kepler and the recently launched

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Transiting Exoplanet Survey
Satellite, TESS. So if you like

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planets – and honestly, who
doesn’t – stay tuned to learn

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more about all sorts of
fascinating new worlds.

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www.nasa.gov/hubble
@NASAHubble