The Week in Space and Physics: Back To The Moon

On Artemis II, the future of NASA, the fate of a comet, and eleven thousand new asteroids

“"We are now falling to the Moon rather than rising away from Earth.” - Christina Koch.

For the first time in half a century, humans have flown over the surface of the Moon.

The moment of closest approach came on Monday evening. After flying for six days, the Orion capsule came within four thousand miles of the surface. From inside the capsule, astronauts were able to view the face of the far side of the Moon, and so observed, NASA said, parts of the lunar surface that had never before been seen directly by human eyes.

Shortly before this close approach, the Orion capsule passed a symbolic milestone by becoming the first crewed vehicle to travel more than a quarter of a million miles from Earth. The astronauts on board Orion thus became the most distant travellers from our planet in all of history.

As they broke this record, Jeremy Hansen – the Canadian astronaut on Orion – paid tribute to the ‘extraordinary efforts and feats’ of their predecessors in space exploration. It would, he hoped, be a short-lived record, one that the next generation of explorers should take it upon themselves to far exceed.

While they passed over the Moon, the astronauts studied the lunar surface and relayed comments back to scientists on Earth. Briefly they also experienced a remarkable solar eclipse, during which they were able to see the solar corona extending around the Moon and observe flashes of small meteorites hitting its surface.

The crescent Earth rising over the moon. NASA.

Overall, the mission has gone better than most people had expected. The launch, on April 1, came within minutes of the launch window opening and placed Orion almost exactly where mission planners had targeted. The capsule itself has performed well, and aside from a few problems with the onboard toilets – not, sadly, uncommon during spaceflight – the life support systems have apparently functioned well.

Engineers did notice issues with helium leaking from propulsion systems at a higher than expected rate. This helium is used to keep the spacecraft’s fuel at the correct pressure, and is normally confined by a set of valves. Though the leak is not an issue for the success of Artemis II, it will likely trigger a redesign for future versions of the capsule.

The next big challenge will be the re-entry. Orion will hit the upper atmosphere at twenty-four thousand miles per hour. It will need to lose almost all that speed in less than fifteen minutes, during which time the capsule will be exposed to a furious heat and pressure. To keep the crew safe, Orion is fitted with a heat shield.

Yet this shield has been a matter of some controversy. During the previous flight of Orion, the shield did not behave as expected. Engineers thus modified the re-entry trajectory of Orion to try to avoid any risk – but this does mean the crew are relying on a shield that has not been fully tested and that may not perform as well as it should.

The risk to the crew, NASA said, is low. But all will no doubt be breathing a sigh of relief as soon as Orion is spotted descending gently towards the waves under a canopy of parachutes.

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Ignition For a New Golden Age?

After Artemis II, what comes next?

At an event at the end of March, NASA laid out an ambitious vision of its future. Key to this is a series of planned missions to the Moon, together involving robotic explorers, crews of astronauts, and the building of a lunar base. But NASA also wants to build nuclear-powered spacecraft and find a new future for the International Space Station.

Under the new timeline, the next Artemis mission will launch in 2027. It will not go to the Moon, but will instead stay in orbit around the Earth. NASA will use the mission to practice docking with the proposed landers – one, Starship, built by SpaceX, and the other, Blue Moon, built by Blue Origin.

Work is already underway to prepare the next SLS for Artemis III. Credit: NASA.

This, NASA boss Jared Isaacman says, will be followed by two missions to the lunar surface in 2028. Both will take crews to the surface, and will be the first of a long series of missions taking place every six months. Alongside these, NASA will send twenty robotic missions to the Moon, including the previously cancelled VIPER rover.

NASA’s Artemis plans had, until now, included a lunar space station called the Gateway. Work on this was proceeding slowly, and it was unlikely to be built until the 2030s. NASA has now called time on it. In place of the Gateway, Isaacman wants to direct efforts towards building a lunar base. It is this project that will be supported by many of the crewed and robotic missions he foresees over the next decade.

Closer to home, NASA has also rethought the future of the ISS. At the moment this is supposed to be retired sometime in the early 2030s. But Isaacman now proposes attaching a new module to the station. This – a core module – will contain the key functions needed to support a space station.

Commercial partners could attach their own modules to it, allowing NASA to build a kind of hybrid commercial station. But it also seems possible the module will help extend the life of the station, and perhaps make it less reliant on the Russian segment. The end result could be an extension of the ISS, or at least a core that could support a new, smaller station in the future.

All this is exciting. But it is also expensive, and far from fully funded. Congress will need to approve the plans and agree to pay for them. That, in a week when President Trump proposed cutting NASA’s budget by a quarter, promises to be the biggest challenge of all.

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Hubble Watches A Comet Die

A year ago, astronomers spotted a comet heading towards the inner solar system. It was named C/2025 K1, and measurements of its orbit soon showed that it was probably a fresh comet, one that had fallen from the distant Oort Cloud and that had never before passed close to the Sun.

Despite its size – the comet measures about five miles across – astronomers thought it was unlikely to survive its encounter with our star. Indeed, at its closest the comet passed closer to the Sun than the orbit of Mercury, and the heat of this close approach placed immense strain on the icy object.

About a month after the comet had passed the Sun, the Hubble telescope captured some images of it. They show the comet breaking up – instead of a single lump of ice, several large fragments were visible. These fragments were not themselves stable. Indeed, even as Hubble watched, one of them broke apart into several smaller pieces.

Hubble’s images of the comet. Image: NASA, ESA, Dennis Bodewits (AU); Image Processing: Joseph DePasquale (STScI)

Thanks to Hubble’s images, astronomers were able to trace back the timeline of just how the comet had disintegrated. Each event in its break-up exposed fresh, pristine ice from its interior, and astronomers now hope to study how this ice behaves as it is exposed to sunlight for the first time.

The surviving fragments of the comet are now heading back towards the outer solar system. A million years from now they may exit it entirely, and then go on to drift through interstellar space. But at least one fragment might remain bound to the Sun. If it does, it may yet return to the inner solar system one day in the far distant future.

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A Flood of New Asteroids

Astronomers working at the Vera Rubin Observatory in Chile announced the telescope had discovered over eleven thousand new asteroids. This haul came even though the observatory has not yet started its main mission, and was based on observations taken during work to optimise its performance.

Among the thousands of new asteroids are thirty-three Near-Earth Objects. As these can potentially threaten Earth – one need measure only a few metres across to cause an impact – astronomers are keen to find and track as many as possible. Fortunately, none of those spotted by Rubin are likely to hit Earth any time soon.

Looking further out, Rubin also saw hundreds of comets and asteroids lying beyond the orbit of Neptune. Only about five thousand such objects are currently known. With the aid of Rubin, astronomers hope to increase that number at least tenfold in the next few years.

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