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Extomoon spotted orbiting alien planet

Exomoons are natural satellites of planets orbiting stars outside our solar system. There is tantalizing evidence suggesting that such a moon has been spotted, 8,000 light years from earth, by the Hubble space telescopes – identifying the first compelling evidence of an ‘exo-moon’. This moon is the size of Neptune, orbiting a planet the size of Jupiter. Both the moon and its planet are thought to be made of gas, rather than rocky like our moon. The researchers estimate that the moon is about 1.5% the mass of its planet – a similar mass ratio to that of our Earth and moon.

This extromoon was discovered on the extra-solar planet Kepler 1625b because of its intriguing anomalies. Transit signals from distant exoplanets are vanishingly small. Exomoons are even harder to detect than exoplanets because they’re smaller, and their transit signal is weaker. And exomoons also shift position with each transit because the moon is orbiting the planet.

There are two lines of evidence:

The moon has not been directly observed (or it’s planet for that matter), which means that it’s existence is indirect. After monitoring the planet’s 19 hour transit across the face of the star, scientists saw a dimming of the star’s light – a common method for detecting the presence of planets. In this case, they saw a second dimming of the host star’s brightness – 3.5 hours later – a pattern consistent with a moon trailing a planet.

The 2nd line of evidence involves a deviation in the timing of the planet’s orbit when Planet 1625b began its transit one hour earlier than predicted, the result of a wobble in its orbit. This was possibly, most likely, caused by the pull of a moon on a planet in the same orbit.

Nailing it down

Kepler-1625b’s host star is sunlike, it’s thought to be about 10 billion years old — more than twice as old as Earth’s star. So it’s much farther along in its life cycle and is therefore probably quite a bit warmer than the sun.

Kepler’s moon remains a candidate – not a confirmed body.

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