Space Sunday: from the Sun to Charon, and the death of a planet

Astrophotographer Mia Stålnacke caught this aurora display over Kiruna, Sweden, in March 2015
Astrophotographer Mia Stålnacke caught this aurora display over Kiruna, Sweden, in March 2015

The Sun is the only star we can directly observe in detail. As such, it has been the subject of study for a long time, significantly so since the birth of the space age. As such, you’d think we know pretty much all there is to know about it; but the fact is that the Sun still has many mysteries – and surprises – of its own awaiting understanding and discovery.

One of these mysteries has been strange particle emissions rich in helium-3. These don’t form part of the more familiar coronal mass ejections (CMEs), which can have an elevated impact on Earth magnetosphere giving rising to more energetic aurorae, or with collimated X-ray flares. The cause of these helium-3 rich outbursts has until now been hard to trace because in order to be detected by the Advanced Composition Explorer (ACE) craft which is designed to study such energetic particles, they have to originate very close to the Sun’s limb, making any associated events hard to observe.

A look at the Sun’s right limb on January 26, 2010. Within the marked red square, a large-scale blast wave travels through the Sun’s atmosphere. These images were obtained with the help of NASA’s STERO A probe and show the Sun’s atmosphere in extreme ultraviolet light.
A look at the Sun’s right limb on January 26, 2010. Within the marked red square, a large-scale blast wave travels through the Sun’s atmosphere. These images were obtained with the help of NASA’s STEREO A probe and show the Sun’s atmosphere in extreme ultraviolet light.

However, on October 13th, two teams of scientists working independently of one another, but using the same data and images gathered from NASA’s STEREO solar observation vehicle and the Earth-orbiting ACE platform, announced they had pin-pointed the cause of the outbursts. They are the result of huge explosions occurring in the Sun’s atmosphere, which in turn create gigantic atmospheric shock waves in the Sun’s atmosphere which can extend over half a billion kilometres (300,000 miles) and advance at speeds of 300 km (190 mi) per second. It is believed the sheer speed of the shock waves from these explosions is sufficient to accelerate  the helium-3 (itself produced as a part of the overall fusion process in the Sun’s core), into a stream of particles thrown off into space.

While it has been confirmed the initial explosions are not related to CMEs or sunspots or other known solar phenomena, the precise reason for the explosions themselves has yet to be determined.

Charon Revealed

Images and data returned by the New Horizons space vehicle at the start of October have provided more details about Pluto’s companion, Charon, revealing it to be an even more fascinating world than had been anticipated.

Charon as revealed in the highest resolution images yet returned of that tiny world by New Hotizons (image: NASA/JPL / JHUAPL / SwRI)
Charon as revealed in the highest resolution images yet returned of that tiny world by New Horizons (image: NASA/JPL / JHUAPL / SwRI)

The images, captured in black and white by the probe’s LORRI camera, have been combined with images and data gathered by the RALPH suite of instruments to present a beautiful full-colour image of almost all of one face of Charon, as seen by New Horizons as it swept through its closest approach to both Charon and Pluto on July 14th, 2015.

Some 1,214 kilometres (753 miles) in diameter, Charon is about half the size of Pluto, and was only discovered in 1978.  Quite how it formed has been the subject of much debate. Prior to New Horizons’ visit, the most popular theory was that Charon coalesced from the debris of a collision between Pluto and another Kuiper belt object. However, New Horizons has so far failed to return any images of Pluto that hint at such a collision, and the make-up of the two worlds is less similar than might be expected were one the offshoot of the other. So the theory gaining ground now is that both bodies were already formed when they fell into orbit around one another.

A comparison of the Moons of Pluto as images by New Horizons, and their relative size
A comparison of the Moons of Pluto as images by New Horizons, and their relative size

The latest images of Charon reveal a striking world, every bit as varied as Pluto, and marked by a massive series of fractures across its midriff, suggesting a massive upheaval in Charon’s past which split open its crust. The southern hemisphere also has a more youthful appearance than the region north of the fracture, suggesting that widespread resurfacing took place following the event, and that cryovolcanism (ice volcanoes) may today be contributing to maintaining the relatively smooth appearance of Charon’s southern regions. So like Pluto, Charon may still be an active world.

New Horizons is now some 3 months past its encounter with the Pluto-Charon system, and travelling away from it at the rate of 52,304 kph (32,690 mph) . On Thursday, October 22nd, the vehicle’s hydrazine manoeuvring system was fired for 16 minutes in the first of four such events designed to position the craft for a close flyby of another Kuiper Belt object, the roughly 30 to 45km diameter 2014 MU69, 6.4 billion kilometres from Earth. If all goes according to plan, New Horizons should make its closest approach to 2014 MU69 on New Year’s Day 2019.

A global map of Pluto has also been released by NASA / JHUAPL - not that all the names shown are informal and subject to IAU approval / change (click for full size)
A global map of Pluto has also been released by NASA / JHUAPL – not that all the names shown are informal and subject to IAU approval / change (click for full size)

Death of a Solar System

570 light years from Earth, a tiny world is dying, being slowly disintegrated by its parent star. It has been spotted by NASA’s Kepler Space Telescope, and confirmed by further earth-based observations of the planet’s parent (and destructive) star.

The planet is roughly the size of Ceres and orbiting a tiny white dwarf star at a distance of approximately 837,000 km (520,000 mi). And when I say “tiny”, I mean a star approximately the size of Earth, and near the end of its life. It attracted astronomers’ attention when Kepler detected a “wobble” it is motion, indicating the star was being influenced by a planet close by. This in itself was significant, as it marked the first time a planet had potentially been identified in orbit around a white dwarf.

Interest in the planet quickly grew when data gathered as it transits across its parent star, which causes the apparent brightness of the star to fluctuate, revealed the transits to be oddly asymmetrical, indicating the planet is trailing a “tail” of debris behind it. Thus, the interpretation is that the planet has wandered too close to its parent, and is slowly being disintegrated by a combination of gravitational influence and the intense heat of the star.

An artist's impression of a tiny world being slowly vaporised by the intense heat from its white dwarf star - something scientists believe they are witnessing via the Kepler space observatory
An artist’s impression of a tiny world being slowly vaporised by the intense heat from its white dwarf star – something scientists believe they are witnessing via the Kepler space observatory

The planet’s destruction is not rapid; it will likely take another million years for it to completely break-up. However, it is helping to further our understanding of white dwarf stars, which mark the end of the life cycle for a main sequence star such as our own Sun.

Around 5 billion years from now, the Sun will exhaust all of its hydrogen fuel stocks. It will then expand into a red sub-giant (gobbling up the inner planets of the solar system in the process), and then go through several stages before becoming a white dwarf. When this happens, any elements heavier than hydrogen or helium should be sucked into the centre of the star; however, spectral observations of many white dwarfs has revealed they have somehow managed to retain heavy elements like magnesium and iron in their atmospheres.

One theory for this is that the heavier elements must be getting constantly added to the star’s atmosphere from the debris rings left by the destruction of any planets which may have once orbited the star. Observations of this break-up present a unique opportunity for this theory put to the test. By watching how this planetary body breaks apart, researchers will be able to get a sense of the different elements inside it as it disintegrates, and how this might affect the composition of the star’s atmosphere.

NASA Seeks to ARRM Itself With Private Sector Help

The Asteroid Redirect Robotic Mission (ARRM) is a proposed mission to spend a robot probe to a nearby asteroid, where it will collect a fairly large chunk (10 metres / 30 ft across) of the rock and then haul it back into cislunar space. Once there, the vheicle and its cargo will be visited by astronauts using the new Orion Multi-Purpose Crew Vehicle.

The mission is being framed as one of the stepping-stones to Mars, which some see as a questionable way of framing things, the first part of which requires the robot vehicle which will actually go out and grab said lump of asteroid, and to this end, NASA has launched a competition for the design of said robot vehicle “bus”.

An artist's impression of the ARRM robot vehicle collecting a sample of asteroid rock
An artist’s impression of the ARRM robot vehicle collecting a sample of asteroid rock

Private sector companies interested in supplying the vehicle have been invited to apply for a Phase 1 Conceptual Studies grant from NASA. Successful applicants will then be entitled to an NASA grant to get them started on actual vehicle design and development, which must be in line which certain NASA requirements. These include the development and use of a high-power solar-electric propulsion system and high-power solar arrays. The completed vehicle should cost no more than US $1.2 billion, and be ready for launch in 2020.

Once the vehicle has reached cislunar space with its sample, it will await the arrival of a 2-person crew aboard an Orion space vehicle, which will be launched atop NASA new SLS vehicle, mostly likely in 2025 as the second crewed mission for the SLS / Orion combination. The crew will rendezvous with the ARRM vehicle and its payload and undertake an examination of the latter, most likely returning samples to Earth.

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