Jupiter has been defeated lately.
In September and October, observers discovered two different asteroids that hit the massive planet just a month apart. While it is not the first time observers have seen such a spectacle, it is quite rare to successfully spot an impact and it can tell us more about the solar system as a whole. And it’s exciting to know that a piece of the universe has just exploded in the atmosphere of the largest planet in the solar system.
“These fireballs are very rare, it’s very difficult to just happen to see them,” Ricardo Hueso, an astronomer at the University of the Basque Country in Spain who studied these sightings, told Space.com. “This year has been exceptional because we usually see one of these effects every two years or so.”
Hit after hit
Despite its rarity, the chances of seeing an impact on Jupiter are higher than anywhere else in the solar system thanks to the enormous size of the planet. Jupiter is both the largest target to hit alongside the sun itself and the most powerful gravitational tug in the neighborhood, increasing its impact rate compared to smaller worlds.
Many of these impacts are discovered by amateur astronomers. Those skilled in the art cannot normally use high powered telescopes for the large amount of time required for such random observations, and the flashes are visible even in small telescopes.
Still, the most recently observed impact was partially discovered by a professional astronomer, Ko Arimatsu of Kyoto University in Japan, who often has a telescope pointed at Jupiter. “When I discovered the impact lightning event through my recognition program, I was amazed,” Arimatsu told Space.com in an email. “The quick find indicates that I was lucky or that the impact rate is much higher than previously expected.”
Arimatsu was also able to observe the event at two different wavelengths, which gave scientists more information about the energy released and the mass of the impactor, Hueso noted. This is a more detailed observation than laypeople can usually contribute.
But other observations were even happier. NASA’s Juno mission, which has been orbiting Jupiter since 2016, happened to fly over the site of the impact just 28 hours later, Hueso said, and his camera took a picture of the atmospheric spot in question from just over 1,200 miles (2,000 kilometers) above Clouds.
“In this picture we don’t see a trace in the atmosphere,” said Hueso. “So this is again an object that is small enough that everything that was released into the atmosphere of Jupiter has dissolved and spread within a few hours through the ambient winds in the atmosphere.”
The impact in September was exceptional not only because of the tight timing, Hueso said. It was also observed by most of the people for such an event and was the brightest fireball lightning seen on Jupiter to date.
“It is probably the largest object we saw when it hit the planet and created a ball of fire that is not big enough to leave anything on the planet for the next few hours or days,” he said, pointing assumed the object was a few dozen feet wide.
As scientists try to discover smaller and smaller objects in the solar system, their targets become more difficult to observe; the same is true when objects are further away. So when it comes to objects that are only tens of meters wide and are in Jupiter’s orbit, which is always at least 350 million miles (560 million km) from Earth, scientists are simply out of luck with spotting them directly.
“Since it is impossible to directly observe meter-sized objects beyond the main belt, their number is unknown,” said Arimatsu. “Jupiter is a natural ‘detector’ for such tiny objects, and the frequency and brightness of the lightning strikes are critical to understanding their size and number density.”
It’s hard to say how many there are to see. “We don’t really know how many millions of objects of this size exist in the solar system, but we are talking about tens or hundreds of millions of objects of this size,” said Hueso.
Timing impacts at Jupiter can help, however. Currently, Hueso estimates that at least about 20 objects hit Jupiter every year – but that includes objects that hit the other side or the poles, where even the most careful examination could not see the lightning bolt. Still, the lightning bolts that mark the demise of these space rocks are one of the few ways scientists can study the smallest asteroids.
“This is the only way we can observe these objects,” said Hueso. “We either observe them when they hit an object and they create, for example, a crater on Mars or a flash of light on Jupiter, or when they come very, very close to Earth.”
The most famous impact on Jupiter was that of 19 fragments of a comet called Shoemaker-Levy 9 in 1994. Scientists discovered the object early enough to see how the planet’s massive gravity tore it apart and the fragments faced their fate.
“I remember the first time I connected to the internet I looked for images of the comet that was about to collide with Jupiter,” said Hueso.
Even as the parts of Shoemaker-Levy 9 reshaped the astronomical community, they also left their mark on Jupiter itself, leaving a dark speck in its clouds that was larger than Earth and visible for months. The darkness was a sign that the debris from the atmospheric explosions of the comet fragments was slowly dissolving and mixing with the outer layers of the cloud.
For Hueso, this trace is one of the main reasons to be interested in impacts on Jupiter. “These objects have been hitting the planet Jupiter for hundreds of millions of years,” he said, “they bring different types of material into Jupiter’s atmosphere, in some ways they contaminate Jupiter’s atmosphere.”
But it’s a rare impact that leaves such a bright scar. Shoemaker-Levy 9 is still the most dramatic impact scientists have seen on Jupiter and one of the few that left visible traces within hours of the collision. Since then, scientists have only discovered smaller objects ending in the giant’s clouds, and they have not seen a scar since 2009, despite the convincing new observations.
“That was the last time. Of all the different impactors that we have discovered since then, none of them left a visible trace in the atmosphere, ”said Hueso. “At least not from Earth.”
Copyright 2021 Space.com, a company of the future. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.