Space Sunday: eyeball worlds, stellar cannonballs, water and rockets

A comparison of sunsets on Earth (l) and simulated on a watery Proxima-b, 4.25 light years away (r). While the parent star, Proxima Centauri, is a lot smaller than our Sun, it would appear much larger in the planet's sky due to the planet being a mere 7 million km from the star

A comparison of sunsets on Earth (l) and simulated on a watery Proxima b as it orbits Proxima Cantauri (r). While the latter is approximately one-seventh the diameter of our Sun, it appears much larger in Proxima-b’s sky, because the planet is just 7.5 million miles from its sun. Credit: PHL Arecibo

In August 2016, I wrote about the discovery of a Earth-size planet orbiting the Sun’s nearest stellar neighbour, Proxima Centauri, a “mere” 4.25 light years away.

The planet, Proxima b, has a mass roughly 1.3 times that of Earth and orbits its dwarf star parent once every 11.2 terrestrial days at a distance of just 7.5 million km (4.7 million miles). It is of particular interest to astronomers because it lies within Proxima Centauri’s habitable zone – the region around a star where it is neither too hot nor too cold for liquid water to exist on the surface of a planet, and where conditions might be conducive for life to arise.

The Earth-sized Proxima-B and its parent star

The Earth-sized Proxima b and its parent star. Credit: AFP

Which is not to say life does exist on the planet. Proxima Centauri is a red dwarf star, just 1.5 times bigger than Jupiter, and stars of that size are subject to massive stellar flares which could easily strip away a planet’s atmosphere, or at least leave it awash in ultra-violet radiation, which is not entirely agreeable for life to arise. What’s more, the planet is liable to be tidally locked with Proxima Centauri, leaving one side baked in perpetual daylight and the other in a frozen night. None of this makes it terribly amenable for life gaining a toe hold.

One of the big questions concerning the planet is how much liquid water it may have. Normally this can be determined by using the planet’s size and mass, and working from there. But while we have an estimate of Proixma b’s mass, there is no definite measurement of its size. Normally, this is done by measuring how much light a planet blocks out, from Earth’s perspective, when it pass in front of its host star. So far, this hasn’t been possible with Proxima b.

In the video above, by the Planetary Habitability Laboratory, Arecibo, the star and orbit are to scale, but the planet was enlarged (x30) for visibility. The planet is represented here as a mostly desert-like, tidally-locked world with shallow oceans and a strong atmospheric circulation allowing heat exchange between the light and dark hemispheres.

Instead, a team at France’s CNRS research institute has been working on simulations based on the “best guess” estimates gathered from the data which is available on Proxima-B, and their findings are intriguing.  This data suggests the planet could be between 0.94 and 1.4 times the size of Earth, depending on  its internal structure.

At the lower end of this scale (planetary radius = 5,990 km / 3,743.75 mi), the CNRS simulations indicate that the planet likely comprises a metallic core surrounded by a rocky mantle, with 0.05% of that mass accounted for by liquid water. While this might not sound a lot, it is worth pointing out that Earth, with a radius of 6,371 km / 3,982 mi has just 0.02% of its mass made up of liquid water. At the upper end of the scale (planetary radius = 8,000-9,000 km / 5,000 – 5,600 mi), the planet likely has a rocky centre surrounded by an ocean up to 200 km (125 mi) deep.

Any significant amount of free water on the planet could mean that the atmosphere is being renewed against loss from solar activity. However, the fact that the planet may well be tidally locked could mean that there is a strong atmospheric circulation between the “dark” and “light” sides of the planet due to the temperature differential between the two, giving rise to massive, hurricane-like storms. A further aspect of tidal locking is that if there is a significant amount of liquid water on the planet, it will have long-since frozen out into ice on the dark side.

Could Proxima-b be an "eyeball" world, staring at its parent star?

Could Proxima-b be an “eyeball” world, staring at its parent star? Credit: Beau, Rare Earth Wiki

This in turn leaves us with the equally intriguing possibility that Proxima-b is a potential “eyeball” world “staring” at its parent star.

“Eyeball” worlds are thought to be  tidally locked planets where the hemisphere facing the parent sun is thought to be baked dry under the unrelenting light of their sun, forming a “pupil”. Around this, close to the the day / night terminator, is an iris-like temperate region of land and water which extends back to the terminator between the day and night sides of the planet, where the water is frozen out into ice, forming the “white” of the “eye”.

None of these most recent findings point to Proxima-b being potentially habitable, and again, it’s worth remembering that even with water and warmth, Proxima b isn’t the most amiable environment in which life might gain a toe-hold. But what they do suggest is that even without life scurrying or swimming about on / in them, exoplanets could be remarkably exotic places, even by our own solar system’s standards.

New Shepard: One Step Closer to Tourist Flights

Blue Origin, the private space company launched by Amazon founder Jeff Bezos achieved another milestone on the road to starting their sub-orbital flights into space for tourists.

On Wednesday, October 5th the company launched another test flight of its New Shephard system of capsule unit and “propulsion module” in order to test the launch abort system of the capsule unit during flight. This system is designed to safely separate the New Shepherd crew capsule from the rocket booster in the event of an anomaly during flight, protecting a future crew and passengers.

The test saw the booster and capsule climb to 4,893 metres (16,053 ft) where, 45 seconds into the flight, the “full-envelope escape system” activated, separating the capsule from the booster, allowing its escape motors on the capsule to fire, accelerating it away from the booster at 400 mph in a 2-second burn. The capsule continued to rise to 7,092 metres (23,269 ft), before it started its decent, the parachute landing system deploying and bringing it to a safe touch-down.

It had been expected that the 70,000 pounds of off-axis thrust delivered by the capsule’s motors would seriously deflect the booster from its flight track and result in its complete loss. However, in a move that surprised many watching, the booster continued upwards to an altitude of 93,713 metres (307,458 ft) where, some 7.5 minutes into its flight, it  re-ignited its motor to execute a controlled vertical descent back to the launch pad and a safe landing.

If all goes according to plan, Blue Origin plans to launch its first passengers on a sub-orbital hop in which they get to enjoy around four minutes of weightlessness, in 2018. The price of tickets has yet to be confirmed. However, competitors Virgin Galactic and XCOR Aersopace are looking to charge US $250,000 and $150,000 respectively, when they commence operations.

Solar Cannonballs

It sounds like the ultimate space weapon from some science-fiction film: a star firing super hot blobs of gas, each twice as massive as the planet Mars and travelling so fast, they’d cover the distance between the Earth and the Moon in 30 minutes; but it’s not science-fiction, it is precisely what is happening 1,200 light years away at a red giant star called V Hydrae – and it has probably been going on for around the last 400 years. But what has been causing them has remained a mystery  – until now.

The plasma “cannonballs” had been detected during two periods of study of the star during 2002 to 2004 and 2011 to 2013 using the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. The study was part of a wider effort to understand planetary nebulae, an expanding shell of glowing gas expelled by a star late in its life.

The "cannonballs" of V Hydrae 1: (1) Studies suggest the red giant has a small companion star in an elliptical around around it. (2) because the star has expanded due to using it's nuclear fuel, the small companion passes through its atmosphere, collecting matter into an accretion disk

The “cannonballs” of V Hydrae 1: (1) Studies suggest the red giant has a small companion star in an elliptical orbit around it. (2) because the star has expanded due to using its nuclear fuel, the small companion passes through its atmosphere, collecting matter into an accretion disk

As a result of the Hubble observations, researchers have been able to compile a detailed map of the blobs’ location, allowing them to trace the first behemoth clumps back to 1986, leading them to believe that a small stellar companion is in an elliptical orbit relatively close to V Hydrae is responsible for their formation.

Because V Hydrae has used almost all its nuclear fuel, it has swollen up into a red giant, causing this small companion to pass through its atmosphere once every 8.5 years, as the smaller star reaches its closest point in it orbit to the larger. When it does so, this smaller star gathers mass from the larger star, which forms an accretion disk around it. When the mass of this disk reaches a tipping point, it acts as a launchpad for the plasma blobs, firing them off in a variety of directions at speeds of around 800,00 km/h (500,000 mph) and with a temperature of 9427o Celsius (17,000o F) – more than twice as hot as the surface of our Sun.

The "cannonballs" of V Hydrae 2: (3) The buildup of material reaches a tipping point, resulting in the ejection of plasma blobs along the star's spin axis. (4) wobbles in the small star's spin and orbit cause the blobs to be "scattergunned" in multiple directions as it moves away from V Hydrae

The “cannonballs” of V Hydrae 2: (3) The buildup of material reaches a tipping point, resulting in the ejection of plasma blobs along the star’s spin axis. (4) wobbles in the small star’s spin and orbit cause the blobs to be “scattergunned” in multiple directions as it moves away from V Hydrae. Image credit: NASA, ESA, and A. Feild (STScI)

In turn, as these blobs spread outwards, they expand and cool, forming and feeding the planetary nebula around V Hydra. As binary star systems are common throughout the galaxy it is thought that this process of forming / feeding planetary nebulae is liable to be common.

Water Under Dione

Water has featured rather a lot in my recent Space Sunday reports. I’ve covered the work in investigating the ocean beneath the ice crust of Europa, one of two moons orbiting Jupiter which is likely to have a liquid ocean beneath its surface (the other being Ganymede). I’ve also covered the thinking around the liquid water ocean under Pluto’s frigid surface. Meanwhile, the Cassini spacecraft, which has been studying Saturn and his moons for the last 12 years (and which is now sadly in the final phase of its operational life) imaged geysers of water breaking through the icy crust of Enceladus, with subsequent confirmation of a global subsurface ocean there.

And it is data from Cassini which has revealed that another of Saturn’s moons, Dione, likely has an ocean of liquid water lying under a thick icy shell. During two close passes of the moon in 2015, Cassini was able to gather data on Dione’s gravity. Using that data, a research team at the Royal Observatory of Belgium were able to build a model of Dione’s likely interior, comparing i directly with that of Enceladus, which happens to be Dione’s neighbour.

NOT an artist's impression. This is an actual image of Dione (foreground) with Enceladus "sitting" on its limb, captured by the Cassni spacecraft on September 8th, 2015. NASA/JPL-Caltech/SpS Institute

NOT an artist’s impression. This is an actual image of Dione (foreground) with Enceladus “sitting” on its limb, captured by the Cassni spacecraft on September 8th, 2015. NASA/JPL / Space Science Institute

This is significant, because Dione and Eceladus share a 1:2 mean-motion orbital resonance, meaning that for every orbit Dione completes around Saturn, Enceladus completes two. As they do so, Enceladus experiences libration (oscillations) as it influenced by both Saturn and Dione. These oscillation, couple with tidal flexing, likely generate heat, which keeps the subsurface ocean liquid.

The model developed by the Belgian team strongly suggests Dione is also experiencing libration, and this is sufficient for the moon to maintain a liquid ocean beneath its 100 km thick covering of ice.

An artist's impression of the interior of Enceladus, shwoing the rocky core, ocean and icy crust. The geysers imaged by Cassini in the moon's southern hemisphere are also show. It is thought Dione has a similar structure, but with a much thicker icy crust

An artist’s impression of the interior of Enceladus, showing the rocky core, ocean and icy crust. The geysers imaged by Cassini in the moon’s southern hemisphere are also show. It is thought Dione has a similar structure, but with a much thicker icy crust

Dione’s ocean has probably survived for the whole history of the moon, and thus potentially offers a long-lived habitable zone for microbial life. “The contact between the ocean and the rocky core is crucial”, said Attilio Rivoldini, one of those involved in the study. “Rock-water interactions provide key nutrients and a source of energy, both being essential ingredients for life.”

Antares Set To Resume Flights

Two years ago, on October 28th, 2014, an Antares booster, built by the private space launch company Orbital ATK  lifted-of from NASA’s Wallops Flight Facility on what should have been a routine flight under NASA’s Commercial Resupply Services (CRS) contract to deliver Cygnus automated resupply vehicle to the International Space Station. Seconds after launch, the vehicle exploded.

October 28th, 2014 and the moment the Antares rocket exploded, as captured on film by Ken Kremer

October 28th, 2014 and the moment the Antares rocket exploded, as captured on film by Ken Kremer

Since that time, Orbital ATK have undertaken a complete overhaul, switching to the use of Russian-built RD-181 rocket motors. It will be put to the test on Thursday, October 13th, when the first of the update Antares vehicles is due to lift-off from Wallops Flight Facility, en route to deliver a Cygnus resupply vehicle to the ISS.

The launch is scheduled to take place a 21:13 EDT on the 13th October, and if all goes according to plan, it will see the Cygnus vehicle rendezvous with the ISS on Sunday, October 16th.

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