Saturn’s shrinking shadow, senior sharks and shooting stars on show

Perseid meteor shower

Late last week, did you stay up late or set the alarm for an early start to see the annual cosmic display of “shooting stars” light up the night sky? 

NASA photographer Bill Ingalls did. He captured this 30-second exposure of meteor streaks across the sky at Spruce Knob, West Virginia.

Known for its fast and bright meteors, the Perseid meteor shower shows up every year in August when Earth passes through a cloud of debris left behind by an ancient comet. This debris field consists of bits of ice and dust – most more than 1,000 years old – which burns up in Earth’s atmosphere to create one of the best meteor showers of the year.

The Perseids have been observed for at least 2,000 years and are associated with the comet Swift-Tuttle, which orbits the sun once every 133 years.

The longest-lived vertebrate award goes to …

A study published in Science looked into the longevity of Greenland sharks – and in the process also found new insights as to when they reach sexual maturity.

The Greenland shark (Somniosus microcephalus) is widely distributed in the North Atlantic, with adults reaching lengths of four to five metres.

Greenland sharks have an extremely slow growth rate of about one centimetre per year, which hinted to researchers that these fish benefit from exceptionally long lifespans.

To determine the average age of this species, researchers used radiocarbon dating techniques on the eye lenses of 28 females. Their analysis suggests the sharks have an average lifespan of at least 272 years.

The two largest sharks measured in at 4.93 metres and 5.02 metres long, which gave them an estimated age of roughly 335 and 392 years old. This places Greenland sharks as the longest-lived vertebrates on Earth.

The study also gave more insight into the age of sexual maturity of the species. Previous reports suggested that female Greenland sharks reach their sexual maturity at when they grow longer than four metres – or around 156 years old. 

Passing of the seasons

The changing length of the shadow of Saturn on the rings marks the passing of the seasons.

Earlier in Cassini’s mission, this shadow stretched across all of the rings. But as the planet nears its northern hemisphere solstice in May 2017, the shadow will shorten further.

At the solstice, the shadow’s edge will stretch just 45,000 kilometres from the planet’s surface, barely making it past the middle of the B ring. 

Supernova ejected from the pages of history

A new look at the debris from an exploded star in our galaxy has astronomers re-examining when the supernova actually happened. Recent observations of the supernova remnant called G11.2-0.3 with NASA’s Chandra X-ray Observatory have stripped away its connection to an event recorded by Chinese astronomers in 386 CE.

The New Chandra data on G11.2-0.3 show that dense clouds of gas lie along the line of sight from the supernova remnant to Earth. Infrared observations with the Palomar 5-metre Hale Telescope had previously indicated that parts of the remnant were heavily obscured by dust.

This means that the supernova responsible for this object would simply have appeared too faint to be seen with the naked eye in 386 CE, leaving the nature of the observed 386 CE event a mystery.

Astronomers were able to compare Chandra observations of G11.2-0.3 from 2000 to those taken in 2003 and more recently in 2013, and measure how fast the remnant is expanding.

Extrapolating backwards, they determined that the star that created G11.2-0.3 exploded between 1,400 and 2,400 years ago as seen from Earth. The revised timeframe for the explosion based on the recent Chandra data suggests that G11.2-0.3 is one of the youngest such supernovas in the Milky Way.

The longest call

Signals transmitted by NASA’s Cassini orbiter at Saturn travelled across 1.44 billion kilometres of space to be received by the European Space Agency’s tracking station at New Norcia, Western Australia, last Friday.

“This was the farthest-ever reception for an ESA station, and the radio signals – travelling at the speed of light – took 80 minutes to cover this vast distance,” says Daniel Firre, responsible for supporting Cassini radio science at the ESA’s operations centre in Darmstadt, Germany.

The signal reception was part of a series of tests to prepare several ESA stations to support Cassini’s radio science investigations, planned to begin later in 2016.