Space Sunday: A pale blue dot, and more on Betelgeuse

A pale blue dot: Earth – the bright dot just right-of-centre – as seen from a distance of 6 billion km (40.5 AU). Credit: NASA / Kevin Gill et al

Thirty years ago, in February 1990, the Voyager 1 space craft had completed its primary mission and was about to shut down its imaging system. However, before it did so, and in response to lobbying from the late Carl Sagan, celebrated astronomer, teacher, broadcaster, writer, futurist and member of the Voyager programme’s imaging team, mission managers order the spacecraft to turn its imaging system back towards Earth to take a final photograph of its former home.

Captured on February 14th, 1990, the image revealed Earth as little more than a tiny blue pixel caught in a  streak of sunlight falling across the camera’s lens. Sagan immediately dubbed the image Pale Blue Dot, and it became his – and Voyager 1’s – Valentine’s Day gift to all of humanity; a last goodbye from the probe taken at a distance of 6 billion km (40.5 AU); 34 minutes later, its camera system was permanently powered down to conserve the vehicle’s power generation system.

From the moment it was published, the image became iconic: a representation of the sum total of humanity, something Sagan recognised at a time when the Cold War still dominated world politics.

Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilisation, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every ‘superstar,’ every ‘supreme leader,’ every saint and sinner in the history of our species lived there–on a mote of dust suspended in a sunbeam.

…It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we’ve ever known.

– Carl Sagan, Pale Blue Dot, 1994

To mark the 30th anniversary of the original image, NASA issued a newly enhanced version of the image, carefully processed by a team led by software engineer and imagining specialist, Kevin M. Gill, seen at the top of this article. It once again reveals just how small and lonely our world really is. And while the Cold War has long since past, in this age of global warming and climate change, this new image of that tiny, pale blue dot and Sagan’s words remain as powerful a reminder of our fragile place in the Cosmos as they did more than two decades ago.

Betelgeuse: Extent of Dimming Revealed

I’ve previously written about the dimming of Betelgeuseas seen from Earth on a couple of occasions over the past few months (see: Space Sunday: a look at Betelgeuse (December 2019) and A farewell to Spitzer, capsules, stars and space planes (January 2020)). Now two images and a video have been released to show just how startling the apparent changes in the star have been over the course of a year.

As an irregular – and massive – variable star, Betelgeuse goes through cycles of dimming and brightening over time. However, what has occurred over the course of the past year is without precedent in the 125-year history of observations marking the star’s behaviour.

Overall, Betelgeuse’s apparently magnitude (brightness as seen from Earth) has fallen by a factor of 2.5 (or roughly 25-30%). This has prompted speculation that the star may have exploded into a supernova – its eventual fate – and we are currently seeing the light, which takes approximately 643 years to reach us, from the run-up to that cataclysmic event. While most astronomers do not believe this to be the case, the two images do present a stunning spectacle of a star in flux.

Side-by-side comparison of Betelgeuse’s dimming, as seen by the SPHERE instrument on ESO’s Very Large Telescope. Credit: ESO/M. Montargès et al.

The images were captured by the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument attached to the Very Large Telescope (VLT, currently the most advanced visible light telescope in the world) operated by the European Southern Observatory Captured in January and December 2019, they not only show just how much  Betelgeuse has dimmed in that time, but also how it seems to have changed its shape.

Again, such changes of shape aren’t unusual for a pulsating variable star like Betelgeuse. The surface of such a star tends to be made up of giant convective cells that move, shrink and swell. However, while these pulses – referred to as stellar activity – have likely been responsible for past changes in Betelgeuse’s shape observed from Earth, they have never been anywhere as extreme as those indicated by SPHERE – although it has been acknowledged that they could also be exaggerated by a cloud of dust ejected by the star long enough ago to have cooled, and is now partially obscuring our view of Betelgeuse.

This December 2019 VLT VISIR image reveals the infra-red light being emitted by the dust surrounding Betelgeuse. These clouds are formed when the star sheds its material back into space, while the black disc at the centre of the image obscures the star and its corona in order for VISIR to see the infra-red light of the dust clouds. Overlaid at the centre of this disc, and to scale, is the SPHERE image of Betelgeuse’s surface, which has a size approximately equal to that of Jupiter’s orbit. Credit: ESO / P. Kervella / M. Montargès / Eric Pantin

The release of the SPHERE images was accompanied by another image of Betelgeuse captured by a further instrument on the VLT, the VLT Imager and Spectrometer for mid-Infra-Red (VISIR).

Also obtained in December 2019, VISIR used a black disc to obscure Betelgeuse to reveal in infra-red the clouds of dust that have been ejected by the star and which expand outwards from it for billions of kilometres. The clouds are a reminder that even before a star like Betelgeuse goes supernova and releases massive amounts of material that may one day produce new stars, it is already pouring vast amounts of material into space that could become the building blocks of life.

Shortlisted: Missions to the Harshest Worlds in the Solar System

On February 13th, NASA announced it has shortlisted four deep space science mission proposals for further funding, up to two of which may be selected for development and flight. All four projects offer compelling targets and opportunities for science and discovery that are not covered by NASA’s active missions or recent selections.

The proposals have been made under NASA’s Discovery Programme, which focuses on planetary science missions that deepen what we know about the solar system and our place in it, with the overall cost of the spacecraft, its science payload, and data analysis at between US $450 million and $500 million.

The four shortlisted missions will received US $3 million to cover a 9-month period to allow them to be further developed and a Concept Study Report to be produced. These reports will be used by NASA to determine which of them will be selected and funded for full development and flight.

An artist’s impression of DAVINCI+ and its descent to the surface of Venus. Credit NASA Goddard Space Flight Centre

The four proposals comprise:

DAVINCI+, the Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging Plus is an atmospheric probe mission proposed by NASA’s Goddard Space Flight Centre to analyse the cloud-wreathed , high-pressure toxic atmosphere of Venus and study the planet’s surface.

Deployed via parachute, the probe would descend through the atmosphere measuring its structure, dynamics and chemistry and use a miniature laboratory modelled after the one carried aboard NASA’s MSL rover Curiosity to take atmospheric samples during its decent and analyse them for their composition, seeking out traces of noble gases, such as xenon, which could reveal insights into Venus’s volcanic and hydrological past.

In addition, a suite of imaging systems, again modelled after those carried aboard Curiosity, would attempt to provide high-contrast images of the terrain below and around the probe as and after it lands.

VERITAS, the Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy is something of a “rival” to DAVINCI+ in that it includes an atmospheric probe.

Proposed by the Jet Propulsion Laboratory, VERITAS primarily comprises an orbiter vehicle designed for a primary 2-year mission in orbit around the planet, tasked to carry out a detailed analysis of the planet’s surface from orbit in an attempt to understand the differences and similarities with Earth, and determine exactly why both planets took such divergent evolutionary paths. In particular, the orbiter would look for signs of current geologic processes and evidence for past or present water.

The atmospheric probe, called Cupid’s Arrow, would take samples during its descent and attempt to analyse them for the presence of noble gases like DAVINCI+, but possibly not all the way down to the lower reaches of Venus’ atmosphere.

An artist’s impression of VERITAS. Credit: NASA/JPL

IVO, the Io Volcano Observer, would be the first mission to explore the most volcanically active place in the entire solar system: Jupiter’s innermost moon, Io. Caught within the complex gravitational tides of Jupiter and those of the outer Galilean moons, Io is literally in a constant state of flux and home to over 400 active volcanoes that are constantly renewing its surface.

IVO would be designed to orbit Jupiter, from where it could make numerous fly-bys of Io over a mission lasting between 5 and 8 years. It would provide new insights into Io’s tidal heating, and how interior heat is generated and spread outwards to the surface. By studying these aspects of the moon’s behaviour, scientists hope to better understand similar processes seen elsewhere, such as on Saturn’s moon Enceladus, which features a warm subsurface ocean.

Trident is the name given to a dual fly-by mission which would have the primary objective of increasing our understanding of Neptune’s largest Moon, Triton with the goal of examining the potential for habitability at the extreme edges of the solar system. Of the four proposals, Trident is the most long-term, as it would not reach its target until 2038.

An icy world, Triton nevertheless appears to have a very active surface – so active, that it is effectively the second youngest of any solid surface body in the solar system after Io. This alone makes it an interesting target of study, as do the facts that it may have a tenuous atmosphere and the fact it probably did not originate in orbit around the planet, but rather started life as a Kuiper Belt object, only to be ejected from there and eventually fall into a retrograde orbit around Neptune.

An animation of Triton’s rotation, compiled from images captured by Voyager 2 in 1989. Credit: PlanetUser / NASA

Like the New Horizons probe to Pluto, the Trident mission would involve a single fly-by of Triton, gaining a boost on its way there from Jupiter, which it would fly-by in a gravity-assist manoeuvre. The probe will pass within 500 km of the moon, allowing it to map Triton’s surface, measure its ionosphere, and hunt for traces of a hidden ocean. As an added bonus, Trident would swing by Jupiter in a fly-by gravity assist to boost it onwards to Neptune.

Which missions have been selected will be revealed in 2021, although it would seem unlikely that both DAVINCI+ and VERITAS will both be funded.

In responding to the NASA announcement of the shortlisting, several space advocates have pointed out that all four missions could be funded for the purchase price of just 17 of the 2,363 F35 fighter aircraft the US DoD has ordered for its air force, navy and marine corps, and when the costs of maintaining a single F35 over its planned operational lifetime is factored in (roughly US $70-$100 million), this number potentially falls to all four missions being funded for the cost of just nine of the aircraft from the DoD’s total procurement. Which tends to put the oft-touted “expensive” cost of space exploration into proper perspective.

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