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The Week in Space and Physics: Dwarf Planet Rings
On a mysterious ring in the Kuiper Belt, a rare supernova, space tourism and Starship
Ever since the demotion of Pluto, the orbit of Neptune has marked a boundary. On one side, facing towards the Sun, lies the realm of the planets. Shepherded by Jupiter, the eight planets here maintain their steady paths through the Solar System. On the other side, looking towards the cold dark of interstellar space, lies the Kuiper Belt.
This region, recent discoveries have found, is home to innumerable dwarf planets. These are too small and numerous to be counted among the likes of Mercury and Saturn, yet too large to be considered as mere asteroids. Largest among them, of course, is Pluto, though another, Eris, appears to be denser and heavier.
Observing these small worlds is hard. Only Pluto and its companion Charon are at all known, thanks to the visit of the New Horizons probe in 2015. For the rest, astronomers must turn to other techniques, either gazing at them through powerful telescopes or watching for subtle signs as they pass in between Earth and distant stars.
This last approach, known as occultation, allows astronomers to study the atmospheres of faraway worlds. As planets pass through starlight, they block and slightly alter the colour of that light. With careful measurement, astronomers can thus build up a picture of how thick those atmospheres are and what they contain.
Recently astronomers used this approach to look at Quaoar, a dwarf planet discovered in 2002. This world, they found, shows no trace of an atmosphere. Yet they did stumble across something unexpected. Moments before Quaoar moved in front of the star being used for occultation, they saw a sudden drop in that star’s light. Afterwards, as Quaoar moved away from the star, the sudden drop occurred again.
This strongly suggests Quaoar is surrounded by a ring. But oddly, the ring is much further from the dwarf planet than it should be. Theory suggests that it should have long ago coalesced into a moon or dispersed into space. Why this hasn’t happened here is unclear.
It is possible that we had good timing: capturing a short-lived ring in the process of forming a new moon. But it is also possible that more is going on than we can see. Quaoar is known to have one small moon, but it may have other undiscovered moons. These could be shepherding the ring's particles, allowing the ring to stay stable.
Rings, in general, are rather mysterious things. Even the famous rings around Saturn are poorly understood: dramatic though they are, theory suggests they too should fade away after a few million years. The discovery of a faraway ring around Quaoar is certainly hard to explain; yet studying it may help us understand those somewhat closer to home.
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Astronomers Spot a Rare Supernova
When supernovae erupt, their light often outshines entire galaxies. Astronomers can thus pick them out at incredible distances, mapping out stars dying a billion light years or more away. Recently, however, astronomers stumbled across a far rarer kind of supernova: one that leaves almost no trace at all.
The star in question belongs to a binary system, one in which a pair of giant stars spent millions of years circling each other. As it began to die, however, it cooled and expanded, a common occurrence in the final years of a massive star. In many binary systems, the partner star may then begin to strip gas away from the dying star, either consuming it or discarding it in space.
In this case the partner star seems to have consumed almost all of the outer hydrogen layers of the star: leaving it far too small to explode in the normal fashion. Instead, its inner core collapsed, forming a neutron star without an accompanying supernova eruption. Such events - referred to as “ultra-stripped supernovae” are thought to be rare: so rare, indeed, that the researchers calculated that just ten similar systems should be scattered across the galaxy.
In this case the story doesn’t quite end here. The neutron star has since turned the tables on its companion, beginning to strip matter away from it and expel it into space. The end result is likely to see a second stripped supernovae take place; leaving two neutron stars locked in orbit.
Eventually that arrangement will come to an end. As neutron stars orbit one another they gradually lose energy, spiralling inwards until they collide. These collisions, known as kilonova, are spectacularly violent and so gravitationally intense that they create ripples in the fabric of spacetime itself.
Yet kilonova are also thought to play an important role in creating heavier, metallic atoms. Indeed, much of the gold, silver and platinum found on Earth may originally have formed in kilonova events. The ultimate death of this binary star system could, then, sow the seeds of future riches.
Space Tourism Grinds to a Halt
A year ago it looked like space tourism was about to take off. Two companies, Blue Origin and Virgin Galactic, had successfully sent astronauts towards the boundaries of space. One, Blue Origin, briefly reached an altitude of 107 kilometres - well over the official one-hundred-kilometre high marker that divides Earth from space.
Both companies seemed poised to follow these achievements with regular flights carrying wealthy passengers. Indeed, Blue Origin did exactly that: sending six crews of tourists into space through 2021 and 2022 and taking bookings for several more flights.
Yet the story for Virgin Galactic was rather different. After the second flight - which carried founder Richard Branson - the company seems to have stalled. A report in the New Yorker claimed that the second flight suffered from technical issues and flew outside of its permitted flight path. Accusations have since arisen that their spacecraft simply isn’t ready, and will need extensive rework before it can carry passengers safely. Whatever the reasons, Virgin Galactic has not flown in over a year.
Blue Origin, too, seems to be facing technical issues. In September last year, an unplanned abort occurred during a mission. Though the empty capsule landed safely, Blue Origin has not flown since. The delay appears to be down to an FAA investigation into the mishap, which will likely have to conclude before Blue Origin can launch again.
That means that potential space tourists have few options at the moment. Neither Virgin Galactic nor Blue Origin seem likely to fly again any time soon. With Russian rockets no longer available, thanks to the war in Ukraine, SpaceX is the only contender still standing.
Starship Fires its Engines
SpaceX has been promising a first launch of their giant Starship spacecraft for over a year now. Though an actual launch date is still to be confirmed, the company last week made a major step towards that goal.
Starship will be powered into orbit by the Falcon Super Heavy rocket, one of the largest rockets ever constructed. At its base are thirty-three engines, all of which need to work together in perfect coordination for a launch. Such a feat has rarely been achieved in the past - the closest contender, the Soviet N1 rocket, had thirty engines, yet failed to ever make it into space.
Last week, for the first time, SpaceX tested firing all these engines together. Though they only managed to light thirty-one - two suffered issues and shut down - their combined performance would have been enough for Starship to reach orbit.
The next step seems likely to be a real launch attempt. No date has been given, but SpaceX president Gwynne Shotwell suggested it could come as soon as March.
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