Astronomers find first evidence for a moon OUTSIDE our solar system: Rocky satellite the size of NEPTUNE is orbiting a gas giant 8,000 light years from Earth
- It orbits a planet called Kepler-1625b which is 8,000 light years from Earth
- Scientists have never before found evidence of a moon outside our solar system
- It is thought to be the size of Neptune and is far larger than any known moon
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Astronomers have found evidence of the first moon to exist beyond our solar system.
The gargantuan ‘exomoon’ is similar in size to the gas giant Neptune and orbits a planet 8,000 light years away called Kepler-1625b.
More than 3,000 exoplanets – worlds orbiting stars other than the sun – have been found so far but no ‘exomoons’ have ever been confirmed.
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This artist’s impression shows what the exoplanet Kepler-1625b (orange) may look like. Its exomoon (blue), the first ever spotted, can be seen orbiting the enormous planet . These objects are believed to be 8,000 light years away from Earth
‘This would be the first case of detecting a moon outside our solar system,’ said Dr David Kipping, an assistant professor of astronomy at Columbia University.
The researchers analysed data from 284 planets discovered by the Kepler telescope that orbit their host star in at least 30 days.
NASA’s Kepler space observatory launched in 2009 on a mission to discover Earth-size planets orbiting other stars.
Kepler looks for the momentary dimming of brightness caused by the transit of a planet and is often a telltale sign of a planet’s existence.
When studying the data from the transit of a planet called Kepler-1625b, the team of researchers noticed some anomalies in the data.
‘We saw little deviations and wobbles in the light curve that caught our attention,’ Dr Kipping said.
As a result of these 2017 findings the team secured a 40-hour window with the Hubble telescope, which is four times more precise than Kepler, to study the potential moon in greater detail.
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Using Hubble, the team observed the entire 19-hour journey of the distant planet across the surface of its star.
Three and a half hours after the completion of the event the team then saw a smaller dip in the star’s brightness, indicating the passing of a smaller object in front of the star.
The astronomers believe that this was the planet’s moon following slightly behind the large planet.
Dr Kipping said of the findings: ‘[It looked like] a moon trailing the planet like a dog following its owner on a leash.’
‘Unfortunately, the scheduled Hubble observations ended before the complete transit of the moon could be measured.’
The study, published in the journal Science Advances, also found that the enormous gas giant planet began its transit 75 minutes earlier than predicted.
This, the scientists claim, further solidifies the theory that that there is a moon orbiting the planet as it implies both celestial bodies are orbiting a common centre of gravity.
This is known in astronomy as the ‘barycentre’ and would cause the planet to wobble from its expected location.
The Hubble telescope (pictured) gives data up to four times more precise than Kepler. It is the most powerful telescope ever built and the researchers observed the entire 19-hour journey of Kepler 1625b in front of its star
Dr Kipping noted: ‘An extraterrestrial civilisation watching the Earth and Moon transit the sun would note similar anomalies in the timing of Earth’s transit.’
This mild deviation in the planet’s orbit could be explained by the gravitational tug from another nearby planet, but astronomers believe there are no other planets in this particular star system.
Lead author Mr Teachey, a graduate fellow in astronomy, said: ‘A companion moon is the simplest and most natural explanation for the second dip in the light curve and the orbit-timing deviation.
‘It was a shocking moment to see that light curve – my heart started beating a little faster and I just kept looking at that signature.
‘But we knew our job was to keep a level head testing every conceivable way in which the data could be tricking us until we were left with no other explanation.’
HOW DO SCIENTISTS STUDY THE ATMOSPHERE OF EXOPLANETS?
Distant stars and their orbiting planets often have conditions unlike anything we see in our atmosphere.
To understand these new world’s, and what they are made of, scientists need to be able to detect what their atmospheres consist of.
They often do this by using a telescope similar to Nasa’s Hubble Telescope.
These enormous satellites scan the sky and lock on to exoplanets that Nasa think may be of interest.
Here, the sensors on board perform different forms of analysis.
One of the most important and useful is called absorption spectroscopy.
This form of analysis measures the light that is coming out of a planet’s atmosphere.
Every gas absorbs a slightly different wavelength of light, and when this happens a black line appears on a complete spectrum.
These lines correspond to a very specific molecule, which indicates it’s presence on the planet.
They are often called Fraunhofer lines after the German astronomer and physicist that first discovered them in 1814.
By combining all the different wavelengths of lights, scientists can determine all the chemicals that make up the atmosphere of a planet.
The key is that what is missing, provides the clues to find out what is present.
It is vitally important that this is done by space telescopes, as the atmosphere of Earth would then interfere.
Absorption from chemicals in our atmosphere would skew the sample, which is why it is important to study the light before it has had chance to reach Earth.
This is often used to look for helium, sodium and even oxygen in alien atmospheres.
This diagram shows how light passing from a star and through the atmosphere of an exoplanet produces Fraunhofer lines indicating the presence of key compounds such as sodium or helium
The moon is estimated to be only 1.5 per cent the mass of its companion planet – which itself is estimated to be several times bigger than Jupiter.
Despite both the moon and the host planet are far larger than Earth and the moon, but the scientists say the mass-ratio between the two is similar.
Exomoons are difficult to find because they are smaller than their companion planet and so their transit signal is weak.
Ideal planets for observation for potential exomoons are in large orbits and have long and infrequent transit times.
In this search, the Neptune-sized moon would have been among the easiest to first detect because of its large size.
The host planet and its moon lie within the habitable zone of the star Kepler-1625 where moderate temperatures allow for the existence of liquid water on solid surfaces.
But Dr Kipping said: ‘Both bodies, however, are considered to be gaseous and therefore unsuitable for life as we know it.’
Future searches will target Jupiter-sized planets that are farther from their star than Earth is from the sun. There are just a handful of these in the Kepler database.
Nasa’s upcoming James Webb Space Telescope could really ‘clean-up’ in the satellite search.
Professor Kipping said: ‘We can expect to see really tiny moons.’
WHAT DOES THE HUBBLE SPACE TELESCOPE DO?
The Hubble Space Telescope (pictured) recently captured a stunning image of a galaxy 20 million light years away
The Hubble Space Telescope was launched jointly by NASA and the European Space Agency.
The Hubble is a space-based and long-term observatory.
The Hubble observes ultraviolet wavelengths, which the atmosphere filters out, and it collects visible light.
‘The Hubble Space Telescope has made some of the most dramatic discoveries in the history of astronomy,’ a statement on the Telescope says.
The machinery sits more than 370 miles above earth.
It can pick up on light via its ‘eyes’, which are five times more focused than ground-based telescopes.
The Hubble focuses on areas in deep outer space ‘where some of the most profound mysteries are still buried in the mists of time’.
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