Venus has no moon, but a modelling study suggests it probably did have one for nearly 2 billion years – before the planet ate it. Understanding this could help us learn about Venus’s previous habitability.

Many large objects probably hit Venus in the early solar system, which could have formed a moon, similar to the giant impact that is thought to have formed Earth’s moon. “There’s a very good chance that Venus did have a moon-forming impact,” says at the University of California, Riverside.

The lack of a moon today is therefore quite unusual, but Kane and his colleagues might have an answer. They modelled what would have happened if Venus did have a moon, and found that in almost all scenarios, it would have been consumed by the planet, long erased from existence by the present day.

Venus rotates quite strangely with respect to the sun, completing a rotation once every 243 days, compared with its orbit of 225 days. This is possibly a result of its thick atmosphere slowing its spin.

In contrast, Earth’s much faster spin transfers angular momentum to our moon, meaning it is moving away a few centimetres each year. For Venus, the opposite would have been true. “The moon is transferring angular momentum inward instead of outward,” says Kane. “It causes the moon’s orbit to catastrophically collapse.”

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The researchers found that at the upper limit of their models, a moon about half the mass of our own could have survived around Venus for 1.7 billion years. At twice the mass of our moon, it would have survived just 30 million years, because of the stronger tidal effect.

Once the moon reached a distance of about 15,000 kilometres, it would have encountered a boundary known as the Roche limit. “That’s where Venus’s gravity rips the moon apart and consumption occurs,” says Kane, with the moon’s debris temporarily forming a ring around Venus until it fell into the atmosphere.

at Washington University in St Louis, Missouri, says the model is interesting but hard to prove. “It’s exceedingly hard to test this idea because there is basically nothing left behind.” This is because Venus’s surface has been repeatedly resurfaced by volcanism, he says.

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Kane, however, says a future mission to the surface of Venus could include a seismometer, a device that measures seismic waves to study the interior of the planet. This could look for evidence of a consumed moon buried underground. “That would tell us a lot,” he says.

If Venus did have a moon, it may have played a role in the planet’s habitability, with Venus once thought to have had oceans on its surface. It is possible a moon could be linked to the planet’s runaway greenhouse effect, in which it lost all its water for reasons unknown and developed a thick, deadly atmosphere.

“If there was an early habitable period of Venus, then the big question is what brought that to an end,” says Kane. A moon crashing into the planet could have evaporated much of its water. “It could definitely be connected to Venus’s runaway greenhouse state,” says Kane.

Part of a discarded SpaceX rocket is believed to have crashed into the moon at 8700 kilometres per hour earlier this morning. Astronomers around the world trained their telescopes on the predicted site of the impact in the hope of capturing images and eking some useful science out of the accidental collision.

The craft is the upper stage of a SpaceX Falcon 9 rocket that launched in January last year carrying the Hakuto-R spacecraft from commercial company ispace – which, ironically, also crashed into the moon during an unsuccessful landing attempt.

It is thought that the almost 14-metre-long, 4000-kilogram Falcon upper stage impacted the moon at 5.35am BST today. The crash was predicted to occur close to Einstein crater, which would place it towards the edge of the visible moon from Earth.

at the University of Leicester, UK, says that telescopes around the world were trained on the site of the impact and that images of the area before and after impact will emerge soon. Lunar orbiters from South Korea and the US will also observe the impact site.

NASA predicts that the impact will have created a crater that is 18 metres wide and 4 metres deep.

“It is not a good thing to be randomly sending debris into the moon,” says Sargeant. “It’s not something we should be making a habit of. What if it hit a site of special interest? What if it caused damage to the historical Apollo landers?”

Both NASA and the European Space Agency are required to take the end of a spacecraft’s life into account before a mission launches, ensuring that there is a plan and enough fuel to safely deorbit it. Commercial companies aren’t covered by the same rules, says Sargeant, although efforts to introduce such requirements are under way.

When SpaceX launched the Falcon in question, the heavy payload required more thrust than usual, meaning that the rocket ended up floating uncontrollably in space. It eventually fell into an orbit that unintentionally put it on a collision course with the moon.

But Sargeant says that some science can be salvaged from the event, with astronomers likely to capture rare images of a moon crater being created and the lunar regolith plumes ejected from the impact.

at the Macau University of Science and Technology, China, says that all planetary surfaces should ideally be kept as pristine as is feasible – without hindering exploration – but that the moon has already been impacted by decades of US, Soviet and Russian, Chinese, Indian, Israeli and other nations’ missions, as well as millions of years of asteroid impacts.

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“Rockets have been landing, crashing and taking off from the surface for decades now,” says Bugiolacchi. A controlled crash may even be welcomed by planetary scientists, he says. “Knowing the projectile’s mass, impact velocity, angle and trajectory provide invaluable data on surface evolution. The primary agent shaping most planetary surfaces is high-velocity impacts. Normally, these events are entirely random in terms of physical properties and dynamics.”

“The moon already has about 100 million natural impact craters of the size expected to be made by this crash, so such a crash will hardly make a difference,” says at the Open University, UK. “I’d be happy with a deliberate collision into the moon if it were done with a science aim and was set up so as to be studied to learn about the moon’s interior or surface composition. However, this crash is accidental and reckless.”

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Titan’s plains may be covered in up to a metre of fluffy, organic “snow”. About 65 per cent of the surface of Saturn’s huge moon is made up of strangely uniform and flat plains, and they seem to be coated in a porous, dry layer of particles that have fallen from the sky.

The surface of Titan is difficult to study from afar because it is obscured by a thick, hazy atmosphere. The Cassini spacecraft, which orbited Saturn from 2004 to 2017, managed to take a closer look using radar. Now, at Cornell University in New York state and his colleagues have analysed the radar data in more detail than ever before.

The way the radio waves from Cassini’s radar instrument bounced off Titan’s surface indicate that the surface isn’t as simple as those of most other rocky bodies in the solar system. “The canonical models that we use to try to understand Titan’s surface, which were developed for the moon and are used for the moon, Earth, Venus – they don’t work directly on Titan,” says Hayes. “Titan is a different beast in terms of the radar-scattering properties of the surface.”

Instead of a simple rocky surface, the radar data was a better fit to a two-layer model, with a blanket of soft, low-density material covering a harder terrain. The blanket layer, ranging from centimetres to a metre in thickness, is probably made up of organic molecules from Titan’s hazy atmosphere, which researchers expect should float down to the surface like snow before getting compacted and solidified over time.

Titan’s surface also experiences rain, wind and erosion, so it is important to understand how the blanket layer has built up slowly over time, shaped by these processes. “But this could give us a hint for how things work more broadly on Titan,” says Hayes.

NASA’s Dragonfly mission, which is expected to launch in 2028 and arrive on Titan in 2034, should be able to measure these layers and help us figure out exactly how they formed. It is crucial not only for our understanding of Titan itself, but also for the design of any future spacecraft that will follow Dragonfly to visit this strange moon and attempt landing there.

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The liquid water ocean hidden underneath the icy crust of Enceladus has long made this moon of Saturn one of the best prospects in the hunt for extraterrestrial life – and it just got even more promising. The discovery of heat emanating from the frozen moon’s north pole hints the ocean is stable over geological timescales, giving life time to develop there.

“For the first time we can say with certainty that Enceladus is in a stable state, and that has big implications for habitability,” says at the University of Oxford. “We knew that it had liquid water, all sorts of organic molecules, heat, but the stability was really the final piece of the puzzle.”

Howett and her colleagues used data from NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, to hunt for heat seeping out of Enceladus. Its interior is heated by tidal forces as it is stretched and crunched by Saturn’s gravity, but so far this heat has only been caught leaking out of the south polar regions.

For life to have developed in Enceladus’s ocean, it would require balance: the ocean should be putting out as much heat as is being put in. Measurements of the heat coming out of the south pole don’t account for all of the heat input, but Howett and her team found the north pole is about 7°C warmer than we previously thought. Combined with the heat radiating from the south pole, that matches the total almost exactly – the ice shell is thicker around the equator, so heat only escapes in significant amounts at the poles.

This means the ocean should be stable over long periods of time. “It’s really hard to put a number on it, but we don’t think it’s going to freeze out anytime soon, or that it’s been frozen out anytime recently,” says Howett. “We know life needs time to evolve, and now we can say that it does have that stability.” Actually finding that life, if it is there, is another story entirely. But both NASA and ESA have missions in the works to look for it over the coming decades.

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