SpaceWrap: Showtime for OSIRIS-REx

NASA’s OSIRIS-REx spacecraft is ready for business. When it descends toward the surface of Bennu next Tuesday, it will be the first time that a US-led mission has attempted to pick up a sample of pristine material from an asteroid.

Since its arrival in December 2018, the spacecraft has been scanning, photographing, measuring and studying the dark rocky rubble pile below, initially from afar, then up close.

Using its laser altimeter instrument (OLA) and data from images taken with its PolyCam instrument, the mission has produced maps with better detail than those of any planetary body ever visited. The primary sample site, inside a crater dubbed Nightingale, was selected based on those maps.

“We spent early 2020 doing low-altitude reconnaissance passes over this site, ultimately imaging at about an eighth of an inch per pixel,” says principal investigator Dante Lauretta. “We basically have incredibly detailed images covering the entire crater, and we counted all of those rocks.”

Shortly before 11am Arizona US time on October 20, thrusters on the spacecraft will fire and gently nudge OSIRIS-REx out of its orbit around Bennu and steer it down toward the rugged surface.

If everything goes well, it will extend its Touch-and-Go Sample Acquisition Mechanism, or TAGSAM, which is suspended at the tip of a 3.35-metre arm. Reminiscent of an air filter used in an older car, it is designed to collect fine-grained material, but is capable of ingesting material up to about 19 millimetres.

Magnetic Moon had our backs

Four billion years ago the Moon had a strong magnetic field that may have helped protect Earth’s developing atmosphere from powerful solar storms, new modelling suggests.

In 1969, the Apollo 12 astronauts discovered that the Moon’s magnetic field is only about one-thousandth that of present-day Earth’s, but recent re-examination of lunar samples using modern techniques suggested it may have been much stronger before waning.

Research also has called into question how the early Earth’s magnetic field alone could have sufficiently protected it from intense bouts of solar wind and radiation.

To investigate, NASA’s James Green and colleagues modelled the overlapping magnetic dipole fields of the ancient Earth and Moon.  At the time, the Moon was much closer to Earth, located only about 18 Earth radii away (compared with roughly 60 today), and its magnetic field was at peak intensity.

The simulations suggest the Moon’s magnetic field acted like a protective bubble, taking the brunt of fierce solar winds and offering Earth’s atmosphere a much-needed extra line of defence. The findings are published in Science Advances.

Long live Betelgeuse

It may be another 100,000 years before Betelgeuse dies in a fiery explosion according to a new international study that also reveals the giant red star in the Orion constellation is smaller and closer to Earth than previously thought.

And part of the reason we know that, says Meredith Joyce from the Australian National University, lead author of the team’s paper in The Astrophysical Journal, is because the supergiant has been behaving strangely lately.

“It’s normally one of the brightest stars in the sky, but we’ve observed two drops in the brightness of Betelgeuse since late 2019. This prompted speculation it could be about to explode.

“But our study offers a different explanation. We know the first dimming event involved a dust cloud. We found the second smaller event was likely due to the pulsations of the star.”

The researchers used hydrodynamic and seismic modelling to learn more about the physics driving these pulsations. This confirmed that pressure waves – essentially sound waves –were the cause, says co-author Shing-Chi Leung from the University of Tokyo.

“It’s burning helium in its core at the moment, which means it’s nowhere near exploding,” Joyce says. “We could be looking at around 100,000 years before an explosion happens.”

Previous studies have suggested Betelgeuse could be bigger than the orbit of Jupiter, but the new study shows it only extends out to two thirds of that, with a radius 750 times the radius of the Sun.

“Once we had the physical size of the star, we were able to determine the distance from Earth,” says László Molnár from the Konkoly Observatory in Hungary. “Our results show it’s a mere 530 light-years from us – 25% closer than previously thought.”

A cluster lacking metal

Astronomers have found a globular cluster (GC) in the nearby Andromeda Galaxy they say contains a record-low amount of metals.

The stars in RBC EXT8 have on average 800 times less iron than our Sun and are three times more iron-poor than the previous GC record-holder. RBC EXT8 is also extremely deficient in magnesium.

“Our finding shows that massive globular clusters could form in the early Universe out of gas with only a small ‘sprinkling’ of elements other than hydrogen and helium,” says Søren Larsen of Radboud University in the Netherlands, lead author of a paper in Science.

“This is surprising because such pristine gas was thought to be in building blocks too small to form such massive star clusters.”

It’s also exciting, says co-author Jean Brodie from Australia’s Swinburne University, because the idea that GC’s have a “metallicity floor” – that they must contain a minimum amount of heavy metals – has “underpinned so much of our thinking about how these very old star clusters formed in the early Universe”.

“Our finding contradicts the standard picture and that is always fun.”

A globular cluster is a large, dense collection of thousands to millions of ancient stars that move together as a tight-knit group through a galaxy.

Larsen and colleagues observed RBC EXT8 using the WM Keck Observatory in Hawaii a year ago, making spectroscopic observations to determine its metal content. They then used three archive images from Canada-France-Hawaii Telescope (CFHT) to determine its size and estimate its mass.