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.
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.
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.
Continue reading “Space Sunday: eyeball worlds, stellar cannonballs, water and rockets”
Inara Pey: Living in a Modemworld 