. But something a kilometer across? Sure.
The other issue is that as objects get smaller they get fainter. Jupiter orbits the Sun 5 times farther than the Earth does, so at best we’re about 600 million kilometers from it, and at worst about 900 million. That’s far enough away that looking for objects in the kilometer size range gets pretty tough.
A new study looked at some images taken of Jupiter back in 2010, and using a clever method the astronomers were able to dig deep to look for faint moons orbiting the giant planet. Cutting to the chase, they found 52 objects that fit their criteria. Seven of those were already known, so it looks like they found 45 potentially new ones.
I love a good coincidence, and this story has two. One is pedestrian, the other cosmic.
It starts with me pondering Gaia data. Gaia is a European Space Agency observatory that is revolutionizing astronomy. Its mission is to accurately map the positions, colors, distances, and motions of over a billion stars yes, a
billion, about 1% of all the stars in our galaxy and create a massive database of the results, essentially a 3D map of the Milky Way galaxy.
And, sometimes, they can solve age-old mysteries. For example, the star Albireo is a close double star, but are the two stars physically related? Astronomers argued for a long time, but Gaia data easily showed that nope, they re not related, at two very different distances but just coincidentally aligned in the sky.
When Voyager 2 passed by Neptune in 1989, the images it returned surprised scientists; it saw an immense oval dark storm in the planet s southern hemisphere as big as Earth itself! Called the Great Dark Spot, it had measured wind speeds of a staggering 2,100 kph, the fastest wind ever measured in the solar system.
Zoom In
The sizes of Earth and Neptune to scale. There s a decent gap there, but not in most exoplanet systems. Credit: NASA / jcpag2012 at wikimedia
But, when Hubble looked at Neptune in 1994, the spot was gone. Poof. Disappeared. Clearly, unlike Jupiter s Great Red Spot, which has persisted for centuries (at least), storms on Neptune evolve on smaller timescales, though they can last for several years. For example, in the same 1994 Hubble observations a smaller dark spot was seen in Neptune s southern hemisphere, one that must have been born in the intervening time between the Voyager flyby and the Hubble images.