Planetary scientists working to establish the origin of a on the evening of 14 September now believe the phenomenon was caused by a small piece of asteroid hitting the atmosphere. The idea that it was space junk re-entering the atmosphere is now looking less likely.

The spectacular event, spotted at about 10pm local time, was caught in numerous videos on social media, which showed a dazzling whitish-green light moving at speed across the sky, in some cases with a trail of glowing material behind it.

At the time of writing,  had been submitted to an international catalogue of fireball events maintained by the American Meteor Society and the International Meteor Organization. Some observers even reported hearing a rumble following the event, which initial analysis suggests occurred over a region near the islands of Islay and Arran in Scotland.

Initially, it wasn’t clear if the fireball was the result of a meteoroid – a natural space rock – entering Earth’s atmosphere and becoming a meteor, or the re-entry of a piece of debris from human space activity, although some early evidence did point to the latter.

“[The fireball] had a very shallow entry angle, a substantial amount of fragmentation, which is typical of space junk, and it looks slowish. Space rocks tend to be a bit faster. However, we’re still crunching the numbers to get a good estimate on the velocity, which will tell us for sure whether this is space rock or space not,” said , a planetary scientist at the University of Glasgow, UK, and member of the UK Fireball Alliance, at the time.

However, a subsequent analysis of the fireball’s path by , a meteor expert at Western University in Canada, indicates that the fireball was the result of a space rock that dived through the atmosphere at a speed of nearly 32,000 miles per hour, or about 51,500 kilometres per hour.

“Meteors typically enter the atmosphere at very high speeds, 75 to 80 thousand miles per hour,” says  at the UK Meteor Network, whose cameras captured the phenomenon. This would equate to between about 121,000 and 129,000 kilometres per hour. “Space junk would be much slower, at maybe 25 to 30 thousand miles per hour depending on the original orbit velocity.”

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NASA’s Juno spacecraft is about to give scientists their closest look at Jupiter’s frozen moon Europa in more than 22 years.

The mission will swoop to around 350 kilometres above Europa’s surface on 29 September, returning detailed images as well as data about the moon’s magnetic field and its icy crust.

The last time a spacecraft got similarly close to Europa was in January 2000 when NASA’s Galileo orbiter swung by at a distance of 351 kilometres.

“We’ve already completed all the preparations. We’re really excited. Everything is on target,” says Scott Bolton, the Juno mission’s principal investigator.

“Our flyby is rather unique. The part of Europa that we’re going to be able to see doesn’t have particularly high-resolution data on it from Galileo, so this’ll be the first time we’ve been able to see that [region] at very high resolution,” he says.

All of Juno’s scientific instruments will be capturing data during the rapid pass, says Bolton. Its main camera, JunoCam, will produce a handful of wide-field views while its navigation camera, known as the stellar reference unit, will be tasked with taking a single, very high-resolution picture of a small patch of Europa’s nightside, lit only by the scattered light from Jupiter’s cloud tops.

Researchers also hope to use the flyby to glean insights into Europa’s ice shell using Juno’s microwave radiometer. Bolton likens the instrument to a radar device, “except it’s passive, so we’re just looking at emission coming out [from Europa] as opposed to sending a signal in and watching it bounce off”, he says. The radiometer’s data could give scientists clues about the depth of the shell and may reveal if there are fractured regions or areas of liquid within the frozen crust.

The team will even look for signs of the water vapour plumes that studies have suggested emanate from Europa, though Bolton stresses that these features “would have to be going off at the right time in a way that we can see them”.

A small asteroid harmlessly collided with Earth on 11 March, creating an explosion in the atmosphere over the Arctic, just hours after astronomers spotted it for the first time.

The space rock, named 2022 EB5, was first detected at around 7.20pm GMT at Piszkéstető Station Observatory in Hungary by an astronomer at Konkoly Observatory in Budapest. Other astronomers were then able to track it before it plunged through the skies to the north-east of Iceland just after 9.20pm GMT. It is one of only five asteroids to have been found and observed before hitting Earth.

“The very rapid dissemination of information from the discoverers allowed other astronomers to make more observations from different vantage points with enough lead time to calculate a precise orbit and its intersection with Earth,” says , an asteroid impact specialist at the University of New Mexico.

Thankfully, the asteroid was sufficiently small that it posed little danger – provisional estimates suggest it was around 1 to 2 metres across.

“Impacts of this size can be considered completely harmless. They typically create so-called ‘airbursts’ at altitudes of about 40 kilometres above ground,” says at the European Space Agency’s Planetary Defence Office.

A signature of the disintegrating asteroid was picked up by infrasound monitoring stations that listen out for pressure waves from nuclear weapons tests. at Western University in Ontario, Canada, who is an expert at interpreting such data, that the energy released by the detonating space rock could have been equivalent to around 2 kilotons of TNT.

Moissl says events like these allow astronomers to make measurements that can shed light on characteristics such as an object’s density or composition. “With only optical observations of asteroids passing by Earth, we might never know more about their physical properties. But if a previously tracked object is also observed during its atmospheric entry and break-up, we can learn more about these quantities,” he says.

Impacts can also give modellers like Boslough a chance to test how well their simulations describe reality. “2022 EB5 was an experiment that nature provided for us,” says Boslough. “The more confidence we have in our models, the better we do our jobs at assessing impact risk for planetary defence.”

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