Space Sunday: exoplanets, greenhouses and meteors

Sunset on an alien world: an artist's impression of sunset on an Earth-like planet orbits our nearest stellar neighbour, Proxima Centauri (seen closest, left), with Alpha Centauri A and B shining in the distance - story below

Suns over an alien world: an artist’s impression of the view from an “Earth-like” planet orbits our nearest stellar neighbour, Proxima Centauri (seen closest, left), with Alpha Centauri A and B shining in the distance – story below. Credit: ESO/L. Calçada

Last week I reported on the latest issue to strike NASA’s Kepler mission to survey other stars for signs of planets orbiting them. On July 28th, during routine communications with the observatory – which is following the Earth around the Sun roughly 121 million kilometres (75 million miles) “behind” the planet – it was discovered the photometer, the camera-like tool used to detect alien planets, had been turned off.

Power was restored to the unit on August 1st, but engineers were still mystified as to why it had turned off in the first place. Communications with the observatory on Thursday, August 11th, confirmed the photometer was still active and Kepler was gathering data, allowing the engineering team to focus on a possible cause for the unit powering off.

The Photometer includes a curved focal plane of 42 charge-coupled devices (CCDs) arranged within 25 individual modules. One of these modules – Module #7 – suffered a power overload in January 2014, disabling it. Most crucially, the failure prompted the photometer unit to power itself off – just as appeared to have happened shortly before July 28th, 2016, suggesting the most recent issue could also be related to the focal plane.

Kepler's focal plane, showing its array of 25 modules, being assembled at Ball Labs prior to Kepler's launch in 2009

Kepler’s focal plane, showing its array of 25 modules, being assembled at Ball Labs prior to Kepler’s launch in 2009

Analysis of the data received following the restoration of power to the photometer reveals that another module, Module #4,  had failed to warm up to the required operating temperature, strongly suggesting it has also failed, and thus triggered the power-down.

As a result, the science and engineering team responsible for the mission have determined that the targets that were assigned to Module #4 will yield no further science results, but this should not impact Kepler’s overall science campaign, which is expected to continue through until 2019, by which time all no-board fuel reserves will have been depleted, and much of Kepler’s work will have been taken over by the James Webb Space Telescope and NASA’s Transiting Exoplanet Survey Satellite (TESS), examined in my previous Space Sunday column.

An “Earth-Type” World Just 4.2 Light Years Away?

Kepler has detected over 4,000 exoplanet candidates, of which around 216 have been shown to be both roughly terrestrial in size and form, and located within the “Goldilocks Zone” (or more formally the circumstellar habitable zone (CHZ) or habitable zone) around their parent star – the region at which planetary conditions could be “just right” for life to arise. Unfortunately, most of these planets are a very long way away. Kepler 425b, for example, regarded as Earth’s (slightly bigger) “cousin”, and the first exoplanet to be confirmed to be orbiting in its star’s habitable zone, is some 1,400 light years away.

However, Kepler is not alone in the hunt for extra-solar planets. Observatories here on Earth are also engaged in the work, both in support of Kepler by undertaking detailed follow-up examinations of candidate stars, and also as part of their own programmes. A recent article in Germany’s Der Spiegel magazine now claims that one of these, the European Southern Observatory’s (ESO)  La Silla faclity, has found an “Earth-like” planet very much closer to home.

Quoting an alleged member of the ESO team, Der Spiegel states the new planet is orbiting Proxima Centauri, our nearest stellar neighbour, a mere 4.25 light years away, and which can be seen in the southern hemisphere night skies. A red dwarf low-mass star roughly one-seventh the diameter of our Sun, or just 1.5 times bigger than Jupiter, it is thought to be gravitationally bound to the Alpha Centauri binary system of stars, frequently the subject of science-fiction stories down through the decades.

The Alpha Centauri system seen through a modest telescope. At the top, slightly left of centre is the Sun-like Alpha Centauri A, to the upper right is the K1 V Alpha Centauri B. The red circle denotes tiny Proxima Centauri

The Alpha Centauri system seen through a modest telescope. At the top, slightly left of centre is the Sun-like Alpha Centauri A, to the upper right is the K1 V Alpha Centauri B. The red circle denotes tiny Proxima Centauri

Given the two primary stars in the Alpha Centauri system are broadly similar to our own Sun  – Alpha Centauri A particularly so – and both are slightly older (around 4.85 billion years), the system has been a frequent subject for study, with the potential for either star to have planetary bodies orbiting it, or given the two stars orbit one another every 79.91 terrestrial years at a distance roughly equivalent to that between the Sun and Uranus, quite possibly around both of them. In fact, two recent papers have suggested two planets orbiting Alpha Centauri B. The first, from 2012, was subsequently dismissed as a spurious data artefact. The  second, from 2015, has yet to be confirmed.

So far, ESO representatives have refused to confirm or deny the Der Spiegel article, or whether an announcement on the matter will be made at the end of August as the magazine claims.  This has been taken by some as tacit confirmation of the discovery, and others that the data – if true – is still being verified. If the latter is the case, some caution at ESO is understandable: the La Silla Observatory was responsible for announcing the 2012 discovery of “Alpha Centauri Bb”, which as noted above, turned out to be a data anomaly.

Some are outright sceptical of the article, pointing out that Proxima Centauri has long been the subject of exoplanet searches by both observatories on Earth and the Hubble Space Telescope, and nary a hint of another other body, large or small, orbiting it has been found.

As a dwarf star – one of the smallest known – Proxima Centauri is also somewhat volatile, with about 88% of the surface active (far more than the Sun’s), and is completely convective, giving rise to massive stellar flares. While this doesn’t out the potential for planets to be orbiting it, the fact that the star’s habitable zone is between 3.5 and 8 million kilometres from its surface, any planet within that zone would be tidally locked to Proxima Centauri, leaving one side in perpetual daylight and the other in perpetual night, with the risk that any atmosphere would be stripped away over the aeons by the stellar flares. So even if the Der Spiegel article is confirmed, it would seem the planet might still be a pretty inhospitable place, even if it is within the Goldilocks zone.

The Oceans of Venus

This image, captured by Japan's Akatsuki mission, shows the night side of Venus under infra-red imaging, revealing the complex interactions going on with the planet's clouds. Credit: JAXA

This image, captured by Japan’s Akatsuki mission, shows the night side of Venus under infra-red imaging, revealing the complex interactions going on with the planet’s clouds. Credit: JAXA

Today, Venus is the hell hole of the solar system. Sometimes referred to as “Earth’s twin” because of their relative similarities in size, mass, proximity to the Sun, and bulk composition, Venus is radically different from Earth in other respects.

For one thing, it has the densest atmosphere of the four terrestrial planets, with a surface pressure of over 90 times that of our own and which is primarily composed (over 96%) of carbon dioxide with an average surface temperature of 735° K (462° C / 863° F). This makes Venus both the hottest planet in the solar system and subject of a runaway greenhouse effect.

Sheathed in an opaque covering of sulphuric acid clouds which hide the surface from view and both reflect sunlight and trap heat beneath them, it’s hard to believe that Venus may, for a time, have been as hospitable as Earth, complete with oceans of liquid water. But this is precisely what a new computer model of ancient Venus suggests.

Until recently, it had been assumed that whether or not a planet has a habitable climate depends on its rotation. If it spins too slowly, as it the case of Venus, where the sidereal day is longer than the time the planet takes to orbit the Sun, it had been assumed the planet may have always had a thick atmosphere, one that in Venus’ case has given rise to its oppressive, destructive environment through most of the planet’s history. However, recent climate studies on Earth has suggested that the atmosphere here could thicken over time under certain circumstances, and give rise to an environment similar to that found on Venus.

One of the rare approximate colour images of the surface of Venus, this one captured on March 1st, 1982 by Russia's Venera 13, which operating for 127 minutes on the surface of Venus - the longest time for any lander to date

One of the rare approximate colour images of the surface of Venus, this one captured on March 1st, 1982 by Russia’s Venera 13, which operated for 127 minutes on the surface of Venus – the longest time for any lander to date

Using this as a baseline, scientists at NASA’s Goddard Institute for Space Studies utilised software tools and algorithms similar to those used to predict future climate change on Earth to explore Venus’ past climate and topography, whilst taking into account the fact that the Sun would have been up to 30% dimmer during the initial two billions years of the planet’s existence. The results revealed that at that time, Venus likely had a much thinner, liquid water-supporting atmosphere, and that while the surface would have had more dry regions than Earth, the planet likely had shallow liquid water oceans sufficient enough to guard against rapid evaporation, with both the water conditions and climate possibly conducive to life.

The model also fits with theories on how Venus developed a runaway greenhouse effect.  Initially, the planet’s slow spin exposed its daylight side to the Sun for two or so months at a time. This warmed the surface, evaporating some of the water to produce rain-giving clouds both cooling the planet and initially shielding it from the slowly brightening Sun.

An artist's impression of how Venus might have appeared some 2.5 - 3 billion years ago. Credit: NASA

An artist’s impression of how Venus might have appeared some 2.5 – 3 billion years ago. Credit: NASA

However, what initially helped cool it eventually led to the planet’s undoing. As the Sun brightens, so too did it heat Venus more, gradually increasing the rate of evaporation. At the same time, increasing levels of ultraviolet light striking Venus’ atmosphere, broke down the water vapour, allowing the hydrogen to escape in space and leaving growing amounts of carbon dioxide behind. These in turn generated more heat within atmosphere, causing more evaporation, thus triggering the cycle which resulted in the Venus we know now.

Persieds

Every July / August, the Earth passes through a haze of stellar debris left by Comet 109P/Swift-Tuttle. The result is of this passage is the Perseid meteor shower (called this because they appear to originate from the constellation of Perseus), is one of the brightest meteor displays one can see in the northern hemisphere. The shower tends to last around a month, from July 17th (ish) through to August 24th, this year rising to a peak on the 11th-12th August, before slowly fading.

The Perseids and where to see them in the night sky

The Perseids and where to see them in the night sky

At the peak of the shower, between 60 and 100 meteors can be seen streaking across the night sky – but 2016 has been an “outburst”, meaning that almost double the average number of meteors might be seen per hour on a clear night. so even though peak activity for the shower has now passed, there’s plenty of good opportunities to see meteors in the night sky in the coming week.

In Europe, the best time to see them is after midnight, while America gets it a little easier and earlier. To check time in your location try timeanddate.com, which should give local observation times.  Of course, you need to be somewhere that’s dark enough to see the night sky without it being blotted too heavily by surrounding Earthly light pollution,  but the Perseids should be visible to anyone with a good, dark view of the night sky. Simply look north-west towards the familiar W of Cassiopeia and then track slightly downwards towards the bright star of Mirfak. This part of the sky is known as the radiant, the point from which the shower appears to originate, so looking towards it offers the best chance of seeing multiple meteors.

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