The Hubble Space Telescope is truly a wondrous thing. Having orbited the Earth since 2009, the images it has captured have been breathtaking. From star nurseries to distant galaxies, its lenses have allowed us to see into deepest space. And in 2017 its high-def range found something that no one had ever seen before…
Hubble had been watching a star in the Cygnus Constellation, about 8,000 light years away. The telescope’s target was the rather imaginatively named Kepler 1625. It was doing this because Columbia University’s Alex Teachey and David Kipping were waiting for an exoplanet – a planet in a different solar system – to pass in front of the star. Such a “transit” can be detected by a slight dip, or wobble, in the light coming from the Kepler 1625.
As expected, the exoplanet – around the same the size of gas giant Jupiter – passed across the face of its star. However, the transit had started over an hour earlier than the astronomers had predicted. And this somewhat premature wobble was followed by a second, entirely unexpected, dip. Had the pair discovered, as they originally might have thought, a new exoplanet? Actually, no. What they’d witnessed was something that nobody else had ever seen.
Of course, the Columbia University pair aren’t the only humans to have looked, really looked, at the wonders of the solar system and beyond. Since Nicolaus Copernicus first accurately described the workings of our local system in the 16th century, we’ve been searching for, and finding, amazing things in the vast extent of space.
Take Jupiter’s Great Red Spot, for instance. The enormous storm, raging on the gas giant for hundreds of years, was first described in 1830. It’s possible, however, that even 17th century stargazers were lucky enough to witness the roiling celestial hurricane. However, in 1979 humans got closer to it than ever before, when NASA’s Voyager 1 took those now iconic images.
Having been a feature of the solar system for so long, however, doesn’t mean that the Spot will be around forever. In fact, the storm, which is large enough to house three Planet Earths, is apparently shrinking. Yes, it seems that over the last century, the swirling red cloud has decreased in width by more than 50 percent. And if the reduction continues, that familiar hurricane will one day be nothing but a distant memory.
Not all significant space discoveries require lots of tech, though. Did you know that Pluto wasn’t found until 1930? And it was discovered with an Earth-bound telescope? On its discovery, it became the ninth official planet in our solar system; however, that distinction wouldn’t last a century. In 2005 when another, larger body, Eris, was found, both were downgraded to dwarf planet status. Our solar system is now officially home to just eight planets.
Not that those eight planets don’t have plenty going on to keep us amazed. Take one of Saturn’s moons, Enceladus. As moons go, it’s quite small and, aside from being one of the brightest bodies in the galaxy, seemed very unremarkable. Until that is, the space probe Cassini took an incredible, explanation-defying picture.
The image, taken with the sun behind the sun behind the satellite, shows great plumes of vapor shooting from Enceladus’ surface. Concentrated at the moon’s south pole, scientists were baffled how such a thing could be occurring on what is essentially a frozen body. The key, it turns out, boils down to two things: eccentricity and water.
Yes, you read that correctly. Water. Scientists believe that the moon’s frozen south pole is hiding an ocean of H2O. As the satellite’s orbit around Saturn is more elongated than circular – known as an eccentric orbit – it moves closer to and then further away from its ringed companion. The gravitational forces produced by these close passes mean that Enceladus literally stretches and shrinks. The friction that is transmuted into heat, which then warms the frozen waters at the pole. That in turn produces the geyser-like spouts so beautifully captured by Cassini.
And then, of course, there’s the tallest mountain in the solar system. Olympus Mons, as it’s known, can be found on Mars, and stands at 72,000 feet tall. It dwarfs Mount Everest, Earth biggest mountain, more than twice over. First observed in the 19th century, it was once a gigantic volcano and covers more than 100,000 square miles of the red planet’s surface. In fact, there are even those who believe that it could once again erupt at some point in the near future. Let’s hope not.
With all of these wonderful discoveries in mind, let’s go back to Teachey and Kepping and that second light change from Kepler 1625. The pair had been looking at data from nearly 300 exoplanets when they came across the new dip. “We saw little deviations and wobbles in the light curve that caught our attention,” Kipping told British tabloid The Sun in 2018. The astronomers are pretty sure that an exomoon caused the anomaly.
“It was definitely a shocking moment. My heart started beating a little faster as I kept looking at that signature,” Kipping went on. Yes, it seems that the pair had discovered the first-ever example of a companion moon in another solar system. According to an article the pair published in the journal Science Advances in 2018, exomoons are so rare that “there are currently no confirmed examples” anywhere in astronomy.
The satellite, similar in size to Neptune, has been nicknamed “Neptmoon.” This makes it bigger than any other moon in our entire solar system, and its location in the Cygnus constellation means that its neighborhood is kind of visible from Earth. And while the pair may not be able to say with absolute certainty that what they’ve found is, in fact, an exomoon, according to Kipping, the find is “exciting, tantalizing, even compelling.”
It seems that the Neptmoon could in fact be a gas giant, like its namesake, rather than a rocky companion, like our own moon. And this could lead to some problems. “If confirmed, this finding could completely shake up our understanding of how moons are formed and what they can be made up of,” Thomas Zurbuchen of NASA told The Sun in October 2018.
And here’s why. As far as we know, companion moons are brought into existence in just three different ways. They can be formed spontaneously out of debris and gas clouds floating in a planet’s orbit. Or they can be knocked out of an existing body by the force of an impact, from, say, a meteor. And third, an existing body can be dragged into a planet’s orbit by gravity. Moons, it seems, are rarely, if ever, made of gas.
So how do Teachey and Kipping know that the Neptmoon isn’t just a gas giant planet orbiting Kepler 1625? Well, technically, they don’t. But they’ve got a pretty good idea. Not only is the transit of the moon and its companion planet bang on for such a twosome, the weight ratio appears to be spot-on as well. Essentially, our moon is just over one percent of the Earth’s mass, and Neptmoon appears to have roughly the same ratio to its planet, Kepler 1625b.
Not everyone is convinced of the Neptmoon’s existence, however. “I remain skeptical,” Rene Heller, astrophysicist at Germany’s Max Planck Solar System Research Institute, said. “If real, [Neptmoon] would be about ten times as massive as all moons and terrestrial planets in the solar system combined,” he told the website Science News in 2018.
“This suggests that the moon would have formed in a completely different way than any moon in the solar system,” Heller continued. Undeterred by the skeptics, however, Kipping was clearly aware of how enormous the find could be, if proven, “We knew our job was to keep a level head and essentially assume it was bogus. [We began] testing every conceivable way in which the data could be tricking us,” the researcher told The Sun.
In fact, just to make absolutely sure that they were right, the pair will have Hubble’s powerful lens trained on Kepler 1625 in May 2019. That’s when the Neptmoon is due to make its next transit across the star. It’s also when we’ll know for sure if Teachey and Kipping’s find will join that list of amazing space discoveries.