Space Sunday: asteroids, telescopes and dust

Credit: Mopic/Shutterstock

Saturday, June 30th marked International Asteroid Day, a global event involving researchers, astronomy groups, space agencies and more talking about asteroids  – and the risk some of them present to Earth.

Since 2013, and the Chelyabinsk event which saw a meteor  roughly 20 metres across, caught on film as it broke up high over the Russian town, the tabloid media has seemingly been obsessed with reporting meteors about to collide Earth and wreak havoc.

Fortunately, the vast majority of the estimated 10 million objects which have orbits passing close to Earth – referred to as NEOs, for Near Earth Objects, are unlikely to actually strike our atmosphere or are of a small enough size not to pose a significant threat if they did, despite all the screaming of the tabloids.

A map showing the frequency of small asteroids entering Earth’s atmosphere between 1994 and 2013. The dot sizes are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy. A total of 556 events are recorded on the map, representing objects ranging in size from 1m to 20m. Credit: NASA’s Near Earth Object (NEO) programme

Which is not to say NEOs don’t pose a potential threat. Not all of the 10 million objects with orbits passing close to, or intersecting, the orbit of Earth have been properly mapped. Take 2018 LA (ZLAF9B2), for example. As I reported at the start of June, this asteroid, some 2 metres across, was only identified a handful of hours before it slammed into Earth’s upper atmosphere over Botswana at approximately 17,000 kilometres per second, to be caught on film as it burnt up. The energetic force of the accompanying explosion has been estimated to have been in the region of 0.3 to 0.5 kilotons (300 to 500 tonnes of TNT).

To offer a couple of quick comparisons with this event:

  • The 2013 Chelyabinsk superbolide (roughly 10 times the size of 2018 LA (ZLAF9B2) disintegrated at an altitude of around at 29.7 km at a velocity between 60,000-69,000 km/h, producing an energy release equivalent to 400-500 kilotons (400,000-500,000 tonnes of TNT). This was enough to blow out windows and send 1,491 people to hospital with injuries, including several dozen temporarily blinded by the flash of the explosion. The first 32 seconds of the video below convey something of the force of that event.

  • In June 1908 a cometary fragment estimated between 60 and 190 metres cross disintegrated some 5 to 10 km above Tunguska, Siberia. This generated an estimated downward explosive force of between 3 to 5 megatons and an overall force of somewhere between 10 to 15 megatons (again for comparison, all the bombs dropped by allied forces in World War 2 amounted to around 3.4 megatons of combined explosive force). This is believed to have generated a shock wave measuring 5.0 on the Richter scale, flattening an estimated 80 million trees covering an area of 2,150 square kilometres. Were it to occur today, such an event would devastate a large city.

There are two sobering points with these two events. The first is that astronomers estimate only about one-third (1600) of objects the size of the Tunguska event meteoroid which might be among that 10 million NEOs have so far been mapped. The second is that many NEOs can remain “hidden” from our view. the Chelyabinsk superbolide, for example passed unseen as the Sun completely obscured its approach to Earth.

There have been several proposals for trying to deal with the potential risk of a PHA – Potentially Hazardous Asteroid – impact over the years. One currently in development is the NASA / Applied Physics Laboratory (APL) Double Asteroid Redirection Test (DART) mission intended to demonstrate the kinetic effects of crashing an impactor spacecraft into an asteroid for planetary defence purposes.

The target for this mission is rather interesting. DART will be launched on an intercept with 65803 Didymos, an asteroid around 750 metres across – but this will not be the vehicle’s target. That honour goes to a much smaller asteroid – around 170 metres across (so in the size range of the Tunguska object) – orbiting 65803 Didymos and informally referred to as “Didymoon”.

Originally, DART was to be a part of a joint NASA/APL and European Space Agency effort, with ESA supplying a vehicle called the Asteroid Intercept Mission (AIM). This would have been launched ahead of DART on a trajectory that would place it in orbit around the 65803 Didymos / “Didymoon” pairing, allowing it to track / guide DART to its target and record the entire impact and its aftermath.

AIM never received funding, leaving the NASA/APL mission, which is currently scheduled for launch in 2021 and will intercept “Didymoon” in 2022. However, in the last few weeks, ESA has announced a revised mission to 65803 Didymos called Hera. Like AIM, it is designed to orbit the asteroid and is moon, and a call has been made to combine it with DART under a new joint mission called Asteroid Impact and Deflection Assessment (AIDA).

This would require DART to be delayed for a number of years to give ESA time to obtain approval for Hera and design, build and launch the craft – so the intercept would not take place until 2026. While this is a delay, it would mean that scientists would be able to better characterise “Didymoon” ahead of DART’s arrival, and witness the impact and its aftermath in real-time.

The original DART / AIM mission – to study the use of kinetic vehicles to divert an asteroid – now potentially superseded by the DART / Hera mission. Credit: NASA / APL / ESA

It’s not clear whether or not DART will be delayed. If it isn’t, then it has been proposed DART carries a camera equipped cubesat similar to those AIM would have used in support of its mission. This could then be separated from DART ahead of the impact so it could image the event as it flies by “Didymoon”. The Hera mission would then arrive a few years after the impact and assess the outcome, including imaging the impact crater on the asteroid and changes to its orbit and its rotation, which can help scientists determine how efficient the impact was in transferring its energy into “Didymoon”.

Continue reading “Space Sunday: asteroids, telescopes and dust”

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Murders, mystery and myths in Second Life

Seanchai Library

It’s time to highlight another week of storytelling in Voice by the staff and volunteers at the Seanchai Library. As always, all times SLT, and events are held at the Library’s home at Holly Kai Park, unless otherwise indicated.

Sunday, July 1st 13:30: Tea-Time at Baker Street

Caledonia Skytower, Kayden OConnell and Corwyn Allen continue with a Seanchai favourite: Tea-time at Baker Street. This time they are going right back to the roots of the legend, and the case which first introduced the world to Doctor John Watson and the renowned Consulting Detective, Mr. Sherlock Holmes.

study-in-scarletA Study in Scarlet was written in 1886 as a full-length novel by Sir Arthur Conan Doyle and published the following year. It is actually one of only four novel-length stories Conan Doyle penned about Holmes and Watson in the original canon (the remaining 56 tales of their adventures are all short stories). As it was the first time the two had appeared in print, part of the story was used to establish each of them, and how they met.

It is 1887, and Doctor John Watson, invalided out of the British Army after being wounded in the Battle of Maiwand during the Second Anglo-Afghan War (1878-1880), has returned to London where he is seeking accommodation. After bumping into an old friend, Watson finds himself being taken to St. Bart’s Hospital, where he is introduced to a stranger carrying out a laboratory experiment. On shaking Watson’s hand, Sherlock Holmes immediately perceives that he has recently returned from Afghanistan, and thus Watson first experiences Holmes’ remarkable deductive abilities – although quite how Holmes came to his conclusion remains a mystery. After a short conversation, he agrees to join Holmes in moving into a flat (apartment) at 221B Baker Street, where they’ll split the rent.

In the story, it is actually several weeks before Watson learns of Holmes’ rather unusual chosen profession. When told, he remains initially dubious until Holmes gives a practical demonstration of his powers of observation and deduction, using a messenger from Scotland Yard as his subject. The messenger has come with a request for Holmes’ assistance; Holmes is at first reluctant to heed the call, but Watson urges him otherwise. So it is that they set out on their first adventure together, one involving poison, a double murder in London and a bitter tale of love, loss and revenge from America.

Join Seanchai for a special 90-minute reading of the final instalment of A Study In Scarlet.

Monday, July 2nd 19:00: Protector

Phssthpok the Pak had been travelling for most of his thirty-two thousand years. His mission: save, develop, and protect the group of Pak breeders sent out into space some two and a half million years previously.

Brennan was a Belter, the product of a fiercely independent, somewhat anarchic society living in, on, and around an outer asteroid belt. The Belters were rebels, one and all, and Brennan was a smuggler. The Belt worlds had been tracking the Pak ship for days — Brennan figured to meet that ship first…

He was never seen again. At least not by those alive at the time.

Join Gyro Muggins as he reads Larry Niven’s engaging tale of humanity’s past – and future.

Tuesday, July 3rd 1900: Walt Longmire

Join Kayden OConnell as he reads more from Craig Johnson’s tales of Sheriff Walt Longmire.

Wednesday, July 4th: No Session.

It’s Independence Day in the United States and Seanchai will be at home celebrating with friends and family.

Thursday, July 5th 19:00: Monsters and Myths  – Procrustes

With Shandon Loring. Also presented in Kitely (hop://grid.kitely.com:8002/Seanchai/144/129/29).

Coming Soon!

July 8th: Tea-Time on the Orient Express

Seanchai Library and friends embark on a literary journey through one of Agatha Christie’s most notable adventures:  Murder on the Orient Express.

Ride aboard the greatest train journey of them all!

Wednesday July 11th: 11:00: Fireside Tales

A new series in a new Seanchai setting – more on this and the Orient Express next week!

 


Please check with the Seanchai Library’s blog for updates and for additions or changes to the week’s schedule.

The current charity is Feed a Smile.