Space Sunday: an eclipse, a star, a moon and an asteroid

Eclipse 2017: the Moon’s umbra passes over the Earth as witnessed by the astronauts aboard the International Space Station, August 21st, 2017. Credit: NASA.

Eyes were on the sky across the world on Monday, August 21st, 2017, either directly or via live stream and television broadcasts, as people watched the 2017 total eclipse of the Sun. Millions of people in the continental United States were particularly well-placed to enjoy the spectacle first-hand as the line of totality tracked diagonally cross the country from Oregon to South Carolina.

NASA reported that some 90 million people viewed their Eclipse 2017 website on the day, with 40 million staying to watch their live stream of the event. Other organisations providing live streams of the eclipse also reported high numbers of hits / views of their coverage.

As one might expect, the event gave rise to some stunning photos and images which have been posted on Pinterest, Flickr, and other photo sharing websites, plus videos and animations. So much so that picking some out to highlight the event is  tough task – I suggest anyone wanting to recapture the event spend time on-line Googling the 2017 eclipse for reports and images. However, there were a couple of images that did leap out to me when looking through reports and photo sites.

The crew of the International Space Station (ISS), Commander Fyodor Yurchikhin and Sergey Ryazanskiy from Roscosmos, Randy Bresnik, Jack Fischer and Peggy Whitson from NASA and Paolo Nespoli from the European Space Agency), witnessed the Moon’s shadow on the Earth three times as the ISS repeatedly crossed the path of the eclipse as the space station orbits the Earth. This resulted in some remarkable images, including the one at the top of this report.

Uncredited image of an airliner passing between the eclipse and the photographer – note the solar prominence at the 1 and 3 o’clock positions. Click for full size.

One of the reasons astronomers are interested in total eclipses is that they provide ideal opportunities for studying the Sun’s corona and prominences – of which there were a number to be observed during this event. This is reflected in the second of my choices (above), which shows two prominences at the one and three o’clock positions rising “above” the Moon’s disk, as an airliner passes through the shot as well.

Jeff Seibert posted a video of images he captured of the eclipse from Santee, South Carolina. These offer a time-lapse of the start of the eclipse, views the famous “diamond ring” which immediately precedes / follows the period of totality and totality itself, revealing the Sun’s corona.

Five eclipses will take place in 2018. Two of these are total lunar eclipses and three are partial solar eclipses:

  • January 31st, 2018: total lunar eclipse, visible from north / east Africa, Antarctica, Asia, Australia, north / east Europe,  India, North America, north / west South America.
  • February 15th, 2018: partial solar eclipse, visible from Antarctica and southern South America.
  • July 13th, 2018: partial solar eclipse, visible from southern Australia
  • July 27th/28th total lunar eclipse: Africa, Antarctica, much of Asia, Australia, much of Europe, southern part of North America, South America.
  • August 11th, 2018: partial solar eclipse, visible from Arctic, north / west Asia, north / east Europe, northern North America.

The next two total solar eclipses will occur on July 2nd, 2019 and December 14th, 2020. he line of totality for both runs across South America.

Tabby’s Star: Giant Ringed Planet to Blame?

I’ve written several times over the last year about the mystery of Tabby’s Star – more formally known KIC 8462852, an F-type main-sequence star located in the constellation Cygnus approximately 1,480 light years from Earth. It’s been of particular interest to astronomers because it experiences massive and irregular dips in brightness of up to 22% at a time, which last for several days before it reverts to its “normal” brightness once more.

Numerous theories have been put forward on why the star is acting so oddly, from the idea that a race of aliens are building a mega-structure – perhaps a Dyson Sphere around it, through to it being a cloud of comets orbiting the star at a great distance, or that it is some kind of “avalanche” type of activity within the star itself.

In April / May, 2017, KIC 8462852 started on a further cycle of dimming, leading to a world-wide bulletin for astronomers to observe it. This resulted in a further theory that the cause of the dimming might be a combination of two clouds of asteroids and a giant ringed planet orbiting the star.

An artist’s impression of exoplanet J1047, thought to have an extended ring system around it. Could a similar planet and ring system account for the fluctuations we see in Tabby’s Star’s brightness? Credit: Ron Miller

This last theory relied on the asteroids occupying the trojan positions either side of the planet as all three orbit the star, making it a complex model. However, another team of researchers from the University of Antioquia in Colombia have now also suggested a ringed planet might be responsible, but in a way which doesn’t require the existence of massive asteroid clouds sharing in the planet’s orbit.

The researchers used data from past dimming events at KIC 8462852 to build a model of the system which shows that a Jupiter / Saturn sized gas giant, orbiting the star at a distance of about 0.1 AU and with an extended Saturn-style system of rings tipped at an angle relative to the planet’s orbital plane around the star could account for KIC 8462852’s apparent fluctuations in brightness.

At such a distance from the parent star, an inclined ring system would not remain relatively constant if form and position, as is the case with Saturn’s rings. Instead, it would undergo short-term changes in shape and orientation as a result of KIC 8462852’s gravitational influence. The researcher’s model shows that these changes would likely lead to changes of the depth of opacity in the ring system, further contributing to the witnessed irregularities in the star’s apparent brightness. As the rings and planet periodically transit between the star and observers on Earth.

A further compelling aspect of this research is that the oscillations in the proposed ring system of any planet orbiting Tabby’s Star could also explain the strangeness witnessed in the  light-curves found in a number of other stars believed to have planets orbiting them. In other words, it is entirely possible astronomers have already observed similar planetary ring systems elsewhere in the galaxy, but simply haven’t been recognised as such.

Like the other theories for KIC 8462852’s behaviour, this latest idea is not definitive; further, better studies of the star – potentially by the James Webb Space Telescope – are required before anything might be known with certainty. However, of all the proposals put forward thus far for the star’s odd behaviour when observed from our solar system, this one does have the virtue of being perhaps the simplest and the first to offer incidental corroboration through the behaviour seen when some other stars believed to have planets orbiting them.

Dragonflies on Titan?

The Johns Hopkins Applied Physics Laboratory, responsible for building a number of NASA space vehicles – most notably in recent years, the New Horizons mission which flew by Pluto – has submitted a novel proposal to NASA for exploring Saturn’s moon Titan.

Called “Dragonfly”, the mission would use a nuclear-powered dual-quadcopter, an evolution of drone technology, carrying a suite of science instruments to study the moon. Capable of vertical take-off and landing (VTOL) operations, the vehicle would be able to carry out a wide range of research encompassing Titan’s atmosphere, surface, sub-surface and methane lakes to see what kind of chemistry is taking place within them.

An artist’s impression of the Dragonfly dual-quadcopter, both on the surface of Titan and flying. The vehicle could make multiple flights to explore diverse locations as it characterises the habitability of Titan’s environment. Credit: JHU /APL / Mike Carroll

Titan has diverse, carbon-rich chemistry on a surface dominated by water ice, as well as an interior ocean. It is one of a number of “ocean worlds” in our solar system that hold the ingredients for life, and the rich organic material that covers the moon is undergoing chemical processes that might be similar to those on early Earth. Dragonfly would take advantage of Titan’s dense, flight-enabling atmosphere to visit multiple sites by landing on safe terrain, and then carefully navigate to more challenging landscapes.

“This is the kind of experiment we can’t do in the laboratory because of the time scales involved,” said APL’s Elizabeth Turtle, principal investigator for the Dragonfly mission. “Mixing of rich, organic molecules and liquid water on the surface of Titan could have persisted over very long time-scales. Dragonfly is designed to study the results of Titan’s experiments in prebiotic chemistry.”

This is not the first aerial mission that has been proposed for Titan, but it is perhaps the most flexible, offering a capable of science platform which would include:

  • A mass spectrometer for analysing the composition of Titan’s atmosphere and surface material.
  • A gamma ray spectrometer of analysing the shallow sub-surface.
  • A seismometer for measuring deep subsurface activity.
  • A meteorology station for measuring atmospheric conditions such as wind, pressure and temperature.
  • An imaging system for characterising the geologic and physical nature of Titan’s surface and identifying landing sites.

Dragonfly has been put forward as a proposal for fourth next round in NASA’s New Frontiers programme, which will see one planetary mission selected from submissions in 2019. Interestingly, the New Horizons project from APL was the first New Frontiers mission to be funded by NASA.

Asteroid to Make Close Pass of Earth

There are over 14,000 known asteroids which orbit the Sun which periodically pass close to the Earth, becoming part if the tens of thousands of Near-Earth Objects (NEOs) occupying teh space around our world. These asteroids vary in size, from very small to quite large. They are a reminder that the space through which the Earth travels is far from empty, and there is a risk of objects passing through it could present a real danger to life here were one to collide with Earth.

On September 1st, 2017, one of the larger (thus far located and tracked) Near Earth Asteroids (NEA) , designated 3122 Florence, will sweep by Earth at a distance of some 7 million kilometres (4.4 million miles), roughly 18 times the average distance between the Earth and the Moon.

An artist’s impression of 3122 Florence passing distant Earth. Credit; NASA

Estimated to be at least 4.4 km (2.7 mi) in diameter, 3122 Florence (named in honour of Florence Nightingale) is just under half the minimum size estimated for the object which gave rise to the Cretaceous–Paleogene extinction event 65 million years ago, which wiped out three-quarters of the plant and animal species on Earth, including the dinosaurs. It was only discovered in 1981, but is to date one of the largest NEAs found. Since its discovery, computer modelling of the asteroid’s orbit shows that the September 1st fly-by will be the closest it has come to Earth since August 31st, 1890, when it swept by at a distance of 6.7 million km. It will not pass this close to Earth again until 2500.

The fly-by presents absolutely no risk to life on Earth, but it does offer astronomers an ideal opportunity to study 3122 Florence in some detail in the hope of gathering more accurate data on its size and composition, and even obtain images of its surface. Amateur astronomers with even modest telescopes and who are in the right locations, will also be able to observe it through early September, as it passes through the constellations Piscis Austrinus, Capricornus, Aquarius and Delphinus, when it will have an apparent magnitude of 8.5.


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