The Week in Space and Physics

On ancient comets, NASA's return to the Moon, an impact on Jupiter and a plan to clean up space

Did an asteroid or comet smash into a town in modern day Jordan several thousand years ago? One recent paper, published in Scientific Reports, argues just that - but the validity of their research, and the biblical speculation they invoke, has been criticised by several other scientists.

The town in question, Tall el-Hammam, stood for thousands of years as the capital of a small city state. Sometime around 1600BC it was suddenly abandoned, and then left unoccupied for centuries. What exactly happened to the town, and the reason for its sudden abandonment, are unclear.

There are, indeed, several possible causes. One, perhaps the most likely, is warfare. The ancient world was a violent place, and it is easy to imagine a victorious army overrunning the town and burning it to the ground. Natural disaster is another possibility. The Jordan Valley, where Tall el-Hammam lay, is prone to earthquakes.

To learn more, a team of archaeologists and researchers from America and Europe took a closer look at the ruins. They report no sign of warfare or violence. There are no arrow heads or sling stones lying in the wreckage, items that would surely have been left behind in any battle. Instead they found evidence of an extraordinarily intense and hot fire.

Buildings, including the palace and city walls, appear to have collapsed in high speed winds. And the ground itself shows signs of a high pressure event, strong enough (they say) to create shocked quartz, a type of rock often found near powerful explosions.

The only possible thing that can explain everything the archaeologists found, according to the paper, is a cosmic impact of some kind. That is, either an asteroid or a comet hit nearby or exploded over the town, creating an intense shockwave that pulverised everything for miles around.

Further support for that idea comes from another town nearby, Tell es-Sultan, which seems to have suffered catastrophic damage and burning around the same time. Evidence shows fires swept through the city, people were hurled into the air and buildings, including a large watchtower, collapsed.

The event may also, the authors speculate, have been recorded in the Bible. In this interpretation, Tell es-Sultan is the biblical city of Jericho, while Tall el-Hammam is Sodom. Sodom, according to the biblical narrative, was destroyed by God, an event described as a rain of fire and brimstone from heaven.

That conclusion, together with some dubious references, has resulted in strident criticism on Twitter and other discussion forums. That criticism has included accusations of faked evidence and incorrect dating of ruins - all casting doubt on the theory that an asteroid or comet was really involved.

Indeed, several of the researchers are associated with religious organisations and universities. The website summarising the archaeological dig speaks explicitly of trying to prove the biblical record. The story of the comet, then, and the link to Sodom, may not be as solid as it first appears.


NASA’s Next Moon Lander

In late 2023 NASA will do something it hasn’t done in almost five decades: land a rover on the Moon. The mission, named VIPER, will hunt for resources on the lunar surface, analysing samples of rock and regolith in search of minerals and water.

In the last few years several probes placed in orbit around the Moon have detected traces of water. Across most of the Moon that water is probably locked up in rocks - solar radiation should long ago have broken down any free flowing water or solid ice on the surface.

Some areas of the Moon are, however, shrouded in permanent darkness. In those places - deep on crater rims, for example - water ice, protected from solar radiation, may have survived. And indeed, several missions over the past few decades have found intriguing evidence that ice does indeed exist in scattered locations across the Moon.

In 1994 the Clementine probe found that the radar signature of deep and dark craters matched that of an icy surface, rather than that of a rocky surface. Later, in 2009, the upper stage of a rocket was deliberately crashed into the Moon; the plume of debris it sent up contained traces of water, and perhaps even of ice crystals.

The evidence is, however, inconclusive, and VIPER aims to take a closer look at one crater in particular to try to settle the question. On September 20, NASA announced that Nobile Crater, near the lunar south pole, had been selected as the landing site. VIPER will therefore spend just over three months scouting out the crater.

Not all scientists are convinced VIPER will actually find ice in Nobile Crater. According to an article in Nature, the crater is indeed thought to contain ice - but only in patches. VIPER may need luck to stumble across ice then - but if it does do so, scientists will be keen to investigate what it finds.

The ice at the lunar south pole should contain a record of the solar system’s history stretching back billions of years. Unlike the Earth, which has a geologically and biologically active surface, features on the surface of the Moon can be extremely old. Ice may, therefore, have lain undisturbed for aeons.

That means it could hold valuable clues to the origin of water, not just on the Moon, but also on Earth. Even so, scientists may need to act fast to protect any discoveries they make. Ice on the Moon will not just be interesting from a scientific viewpoint; it will also be a vital resource for future human visitors.


Amateurs Spot an Impact on Jupiter

Astronomy is one of the few scientific fields in which amateurs still regularly make contributions. In recent years amateur astronomers have been the first to spot events as varied as supernova and comets. That is, partly, because of the sheer size of the universe around us - but also because much of it is visible even without sophisticated equipment.

In the latest example of amateur discoveries, five astronomers in Europe and South America reported seeing an asteroid or comet smash into Jupiter. The impact happened on the evening of September 13th, and appeared as a two second long flash of light.

Analysis of the imagery recorded suggests the object was about twenty meters in length, and it was probably the remnant of a larger object that shattered into pieces as it was dragged into Jupiter’s grasp. In that, the collision is somewhat reminiscent of the 1994 impact of Shoemaker-Levy 9, a comet that fragmented and then left several large impact spots across the giant planet.

The initial discovery of this new impact came thanks to a piece of software developed by Marc Delcroix, a French amateur astronomer. His software, DeTeCt, is specifically designed to analyse footage of Jupiter and Saturn in search of such impact events. In this case, a Brazilian astronomer, José Luis Pereira, ran his footage through the software - which reported a high chance he had found an impact.

After news of his observations spread, several other amateur astronomers realised they, too, had captured the event on film. At least nine separate observations were made, which, according to Delcroix, makes this the most watched impact event on Jupiter in more than two decades.

Delcroix’s DeTeCt software is freely available on the project’s website. The site also features a nice description of the impact event, and collects the known amateur footage of the collision.


Cleaning up Space Debris

Space debris is a growing problem. Tens of thousands of objects now circle our planet, and almost all of them are dead satellites, spent rocket bodies or fragments left behind from collision or explosions. Only a small fraction - less than a fifth of all tracked objects - are active satellites.

That is a major problem for satellite operators. A collision in space - even with a small fragment of debris - is extremely energetic. The result, almost inevitably, is the destruction of the spacecraft - an event that not only wipes out a valuable asset for a satellite operator, but also adds to the growing pile of debris.

The solution to this problem is not obvious. Operators have little incentive to clean up after themselves - doing so would, presumably, require using limited fuel reserves, adding costs that many would rather avoid. Actively removing old debris is hard, expensive and fraught with legal questions - who, for example, has the right to take down an old satellite?

Even so, the importance of the challenge means that space agencies are now starting to look for solutions. Last year the Japanese Space Agency, JAXA, awarded a contact to Astroscale, a company dedicated to both extending the life of existing satellites, and cleaning up old ones.

The mission, planned to launch in 2023, will see Astroscale’s satellite rendezvous with an old rocket body, photograph it and then attempt to remove it from orbit. It will do that by using its own propulsion system to slow the rocket body down, thus, thanks to the laws of orbital mechanics, dragging it back down into the atmosphere.

Astroscale’s solution is unlikely to do much to clean up space. They may be able to remove a few of the biggest, and perhaps most concerning, pieces of debris. That, though, will do little to clean up the thousands of small fragments now circling our planet. Getting rid of them will take another, more ambitious, approach.


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