Space Weather in Wartime: A Sunspot Detonates Naval Mines

Nov. 9, 2018: Rewind almost 50 years. On Aug. 2nd, 1972, giant sunspot MR11976 began to explode. For the next 2 days it unleashed a series of X-class flares, causing deep radio blackouts on Earth and punishing the solar panels and onboard electronics of satellites in Earth orbit. One CME (cloud of plasma) rocketed across the sun-Earth divide in only 14.6 hours–a record that still stands today. Resulting geomagnetic storms sparked auroras so bright, they cast shadows in countries as far south as Britian.


Above: Images of giant sunspot MR11976 from the Paris Observatory. [more]

The 1972 solar storm is legendary at NASA because it occurred in between two Apollo missions: the crew of Apollo 16 had returned to Earth in April and the crew of Apollo 17 was preparing for a moon landing in December. If the timing had only been a little different, astronauts could have been sickened by radiation, requiring an emergency return home for medical attention.

Turns out, it’s legendary in the Navy, too. According to a research paper just accepted for publication in the journal Space Weather, declassified Naval archives reveal an extraordinary explosion in the sea lanes near Vietnam: “On 4 August (1972) TF-77 aircraft reported some two dozen explosions in a minefield near Hon La over a 30-second time span…Ultimately the Navy concluded that the explosions had been caused by the magnetic perturbations of solar storms, the most intense in more than two decades.”


Above: A magnetogram from Manilla reveals unusual disturbances on Aug. 4-5, 1972. [more]

The authors, led by Delores Knipp of the University of Colorado, continue: “Aerial inspections revealed additional evidence of detonations elsewhere along the coast. The wartime memoirs of a US Navy Mineman-Sailor, Chief Petty Officer Michael Gonzales,state: ‘During the first few weeks of August, a series of extremely strong solar flares caused a fluctuation of the magnetic fields, in and around, South East Asia. The resulting chain of events caused the premature detonation of over 4,000 magnetically sensitive [mines].'”

This prompted the Navy to fast-track the replacement of magnetic-influence-only mines with mines that also required seismic or acoustic triggers during periods of high solar activity.

The August 1972 storms affected Earth in ways that are are only now being fully understood almost 50 years later. Moreover, Knipp and colleagues say the storms could be a previously-unrecognized example of an extreme Carrington-class event, and they urge further scrutiny. Given the experience of the US Navy, who can argue? Read the original research here.

Did an Alien Light Sail just Visit the Solar System?

Nov. 6, 2018: It sounds like a tabloid headline, but in this case it could be real. Mainstream researchers from the Harvard Center for Astrophysics have made the case that interstellar asteroid ‘Oumuamua could in fact be an alien light sail. Their original research was posted Oct. 31st on the moderated preprint server arXiv.org.

The story of ‘Oumuamua begins in October 2017 when it was discovered by Robert Weryk using the Pan-STARRS telescope atop Hawaii’s Haleakalā volcano. Astronomers quickly realized that ‘Oumuamua was something special: The object was hurtling through the Solar System on an unbound “hyperbolic” orbit. It came from the stars. Dramatic changes in the object’s brightness suggested that it was tumbling and asymmetric–thin and wide like a cigar or perhaps a pancake.

oumuamua

This artist’s concept shows how ‘Oumuamua is usually depicted: as a cigar shaped asteroid.

On its way out of the Solar System, something unexpected happened. ‘Oumuamua accelerated as if jets of gas were pushing it forward. Astronomers who initially thought ‘Oumuamua was an asteroid now turned their attention to the comet hypothesis. Comets naturally develop jets after close approaches to the sun, and such jets could explain ‘Oumuamua’s behavior.

Just one problem: “Despite its close Solar approach of only 0.25 AU (inside the orbit of Mercury), ‘Oumuamua shows no sign of any cometary activity, no cometary tail, nor gas emission/absorption lines,” point out the Harvard researchers Shmuel Baily and Abraham Loeb. Moreover, “if outgassing was responsible for the acceleration, then the associated torques would have driven a rapid evolution in ‘Oumuamua’s spin, incompatible with observations.”

So if it’s not an asteroid, and it’s not a comet, what could it be? Loeb, who is the chair of the astronomy department at Harvard University and also chairs the advisory board for the Breakthrough Starshot light sail project, realized that the acceleration profile was key. The non-gravitational acceleration of ‘Oumuamua scaled with distance from the sun (r) as r-2 — just like a light sail would behave.

comethypothesis

The comet hypothesis. Credit: NASA/JPL-Caltech

Modeling ‘Oumuamua as a thin object pushed by solar radiation pressure, Baily and Loeb found that it would fit the observations if it were a sheet of material 0.3 mm to 0.9 mm in thickness with a mass surface density of ~0.1 grams per square cm. “Although extremely thin, such an object would survive an interstellar travel over Galactic distances of  about 5 kiloparsecs, withstanding collisions with gas and dust-grains as well as stresses from rotation and tidal forces,” they wrote.

The researchers are now calling for more observations to look for ‘Oumuamua-like visitors to the Solar System. They could be natural objects created by some unknown process in the interstellar medium–or they might be artificial. “A survey for lightsails as technosignatures in the Solar System is warranted, irrespective of whether ‘Oumuamua is one of them,” they conclude.

Although technical, Baily and Loeb’s paper is well written and unusually readable for nonspecialists. Check it out.