The “Earthlike” Planet of Proxima Centauri

The steady improvement of techniques for detecting extrasolar planets has borne fruit—and a low-hanging fruit at that.  The nearest star to the Solar System, Proxima Centauri, has been found to have a planet (imaginatively named Proxima Centauri B) with roughly Earth-like size and even Earth-like temperatures.  This is fascinating news, but what does it really mean?  Is this really another Earth?

The press has been all over this story, and some of what has been written makes sense.  But what reliable knowledge do we have?

First, this is indeed a rocky terrestrial-type planet.  It is the closest known planet to the Solar System, and indeed orbits the star that is the Sun’s nearest neighbor.  Interstellar distances, even for nearest neighbors, are huge: Proxima Centauri (let’s call it Proxy) is 4.24 light years away from us, a dizzying 270,000 Astronomical Units (1 AU is the mean distance of Earth from the Sun).  That’s 64,000 times as far as Jupiter is at its closest to Earth. 

The mass of the planet is estimated to be 1.3 times the mass of Earth.  Its radius and density are unknown.  It orbits once every 11.2 Earth days at an average distance of 0.05 AU from Proxy, following a path whose eccentricity is so far unknown.  Proxy is a faint red Main Sequence star, of spectral class M6, with a mass of about 0.123 times the mass of our Sun and a luminosity only 0.17% of the Sun’s—but almost all of that light (about 86% of it) is infrared (heat) radiation invisible to the human eye.  It is a member of the family of flare stars, undependable neighbors that emit powerful and unpredictable flares. The star’s photosphere (its visible surface) is at a mere 3000 Kelvins, cool enough for “clouds” of refractory metals and oxides to form. 

It is likely that Proxy orbits around the common center of mass of the Alpha Centauri (α Cen) system, but far enough from α Cen that its orbital period must be on the order of a million years.

A planet forced to live in such close proximity to its star suffers a variety of indignities.  The first is that the erratic activity of the star subjects the planet to extreme brightness fluctuations and to bombardment with high fluxes of X-radiation near times of maximum activity.  The second is that tidal friction can quickly despin the planet, causing a rotational lock between the star and planet.  Third, if the planet is too close to its star, the planet may cross the Roche limit and be torn apart by the star’s tidal forces.  Proxy B certainly suffers from the first of these afflictions and certainly does not suffer from the third: if it were inside the Roche limit there would be no planet to detect, only a debris disk; a super asteroid belt.  The intermediate fate, falling into a rotational lock, is unavoidable in such close quarters, but there are several distinct outcomes with very different significance, and for which we presently lack the data to choose between them. 

The simplest possibility, if the orbit of Proxy B is nearly circular, is for it to simply lock directly onto Proxy and always keep the same face toward its star.  With the Sun shining on only one side of the planet, the sub-solar point would be quite hot, and half of the planet would be frozen in eternal night.  Volatile gases would migrate into the darkness and freeze out on the surface, making vast deposits of water ice, carbon dioxide ice, and other gases, and perhaps generating lakes of liquid argon and the heavier inert gases krypton and xenon.  Nitrogen and oxygen, if present, would fall as snow on the night side.  Any slight eccentricity of the planet’s orbit would cause it to rock back and forth once per year (in the case of Proxy B, one year is just 11.2 Earth days). The strong solar tidal forces on the planet would cause the rocking to damp out and the orbit to become more perfectly circular.  This is called a 1:1 spin-orbit resonance, like the Moon around Earth or many satellites of the outer planets around their primaries.

But we have no guarantee that the planet’s orbit is closely circular.  A sobering example is provided by Mercury, a tidally despun planet locked onto its star (the Sun) but with a significant orbital eccentricity.  It actually rotates in a 3:2 spin-orbit resonance: three planetary rotations in two planet years.  At consecutive perihelion passages, opposite points on Mercury’s equator face the Sun.  Thus two regions get alternately scorched—and frozen.  Because of the gravitational stresses, the planet ends up slightly elongated with two bumps on opposite sides of the planet’s equator.  At perihelion passage the angular rate of rotation of Mercury and its angular rate of motion along its orbit are almost exactly equal, so that the “hot pole” tracks the Sun rather closely for many days near perihelion.  Other resonant relationships besides Mercury’s 3:2 resonance are also possible, but they have the potential for disaster: 2:1 and 5:2 and 3:1 resonances are associated with such large orbital eccentricities that they raise the potential for collision with other planets.  Note that 2:1 and 3:1 resonances would have the same spot on the equator being baked on each perihelion passage; 3:2 and 5:2 resonances would have the strongest heating localized alternately in two regions on opposite sides of the planetary equator. 

We don’t yet know the orbit of Proxy B well enough to distinguish between these different states.  But we can see that some of these states would generate extreme temperature and weather behavior that would not be conducive to maintaining a biosphere—and that’s without even considering the effects of wild luminosity and flare activity by the star.

Oh, and one other thing: Proxy B is so close to its star that it is quite near the point at which the tidal forces of its star would disassemble the planet and turn it into an asteroid belt.  Bummer.

But if the planet is in, say, a 3:2 resonance--and all its volatiles don’t go gentle into that good night—the star will remain on the Main Sequence, providing heat to its planets, for another 4000 billion years.  No need to rage against the dying of the light.

Women in Space

About three years ago, shortly after the launch of the Chinese Shenzhou 9 spacecraft in 2012 with female “Taikonaut” Liu Yang aboard, I was interviewed on television by a woman reporter who seemed quite impressed by the fact that China had a real female astronaut.  She was aware that the first female space traveler was Valentina Tereshkova, who flew a mission in the Soviet Union’s Vostok program ‘way back in 1963, and wondered why the United States didn’t have female astronauts.

I was confounded by the question: it was like being asked why gravity had stopped working, or whether I had stopped beating my wife!  Perhaps a little summary is in order here.

The first woman to travel in space was indeed Valentina Tereshkova.  I actually would hesitate to call her an astronaut; “state-sponsored space tourist” would be a better description.  Her employment as a textile worker seemed poor preparation for piloting a spacecraft: she was not trained as a pilot, engineer, or scientist.  According to my Russian friends, she was trained in space flight to the extent of being “warned not to touch anything”, which I view as a probable overstatement by jealous men.   However, she had a background as a parachutist, an important factor.  The rationale for flying a parachutist was explained as giving her the option of jumping out of the Vostok capsule “if something went wrong”.  (In reality, it was always far safer to jump out than to remain aboard, because the spherical Vostok capsule and its Voskhod successor had the nasty habit of rolling downhill upon touchdown, much to the detriment of their occupants.)

The argument that Tereshkova was pioneering the way for Soviet women astronauts is ludicrous: the next Soviet woman cosmonaut was not to fly for another 19 years!  That woman, Svetlana Savitskaya, flew on the Soyuz T-5 mission to the Salyut 7 space station in July, 1982.   She was a real astronaut, well trained and competent to do far more than touch the controls.  Two years later she flew a second time, on the Soyuz T-12 mission, becoming the first woman to fly in space twice and also the first woman to go on a spacewalk. 

In 1978 NASA had selected a new class of astronauts, including several women.  It was clear that by 1983 NASA would begin launching female astronauts into orbit.  It is reasonable to interpret Savitskaya’s flight as being a preemptive strike, timed to beat NASA’s women astronauts into space-- but she was a real astronaut!

The first American woman to fly in space, Sally Ride, a Ph. D. physicist from Stanford, flew two Space Shuttle missions (STS 7 and STS 41G, in 1983 and 1984 respectively).  She was followed in quick succession by Judith Resnik (STS 41D and STS 51L in 1984 and 1986) and Kathryn Sullivan (three flights, STS 41G, STS 31, and STS 45 in 1984, 1990, and 1992, plus one spacewalk).  Anna Fisher flew on STS 51A in 1984, and Margaret Seddon flew three STS missions between 1985 and 1993. 

Shannon Lucid flew five separate space missions between 1985 and 1996, the last being a visit to the Mir space station.  She also has the unusual distinction that she was the first woman born in China to fly in space.

Bonnie Dunbar followed with five Space Shuttle missions from 1985 to 1998, and a number of other American female astronauts have flown three, four, or five missions since that time.

As of April 2016, the totals look like this:

·       Forty-four American women have flown in space, for a total of 116 missions.

·       Four Soviet/Russian women (Valentina Tereshkova, Vostok 6; Svetlana Savitskaya, Soyuz T 5, Soyuz T 12; Yelena Kondakova, Soyuz TM 20, STS-84; Yelena Serova, Soyuz TMA 14M) have flown a total of six missions.

·       Two Canadian women (Roberta Bondar, on STS 42; Julie Payette on STS 96 and STS 127) have flown a total of three Space Shuttle missions,

·       Two women from Japan (Chiaki Mukai on STS 65 and STS 95; Naoko Yamazaki, STS 131) have also flown a total of three missions.

·       Two Chinese women (Liu Yang, Shenzhou 9; Wang Yaping, Shenzhou 10) have each flown one mission. (The political significance of the launch of China’s first female space traveler can be judged by the fact that it occurred precisely on the 49^th anniversary of the launch of Valentina Tereshkova.)

·       From France (Claudie Haigneré, Soyuz TM 24 and Soyuz TM 33), two missions.

·       From India (Kalpana Chawla, STS 87 and STS 107), two missions.

·       From the United Kingdom (Helen Sharman, Soyuz TM 12), one mission.

·       From Iran (Anousheh Ansari, Soyuz TMA 9), the first female space tourist, an Iranian-born US citizen, one mission.

·       From Italy (Samantha Cristoforetti, Soyuz TMA 15M), one mission.

·       From the Republic of Korea (Yi So-yeon, Soyuz TMA 12), one mission.

Soviet/Russian boosters have launched 6 American women (7 counting Anousheh Ansari*), 4 Russian women, 2 French women, and one woman each from Great Britain, Iran*, Italy, and Korea. 

If a woman wants to fly into space on a Russian booster, her best bet is to be an American citizen.

Of the 139 missions flown by women, 84% have been by Americans and 4% by Russians.

A Reason to Want Global Warming

Those of you who do not read the Journal of Geography and Natural Disasters before breakfast each morning missed something interesting.  On 17 March that journal published a paper by M. J. Kelly of Cambridge University on the subject of “Trends in Extreme Weather Events since 1900- An Enduring Conundrum for Wise Policy Advice”.  Now, we know that human activities have added a lot of carbon dioxide to the atmosphere since 1900, and we know that CO₂ has a net warming effect on the planet.  Numerous press reports have claimed that global warming must cause an increase in the frequency and severity of extreme weather events.  Interestingly, the Intergovernmental Panel on Climate Change (usually familiarly referred to as the IPCC), which has consistently warned about anthropogenic global warming (AGW), has never endorsed this position. 

Global warming, according to both model calculations and observations, causes the most warming at higher latitudes and the least warming near the equator.  In the language of meteorology, the meridional temperature gradient (the temperature contrast between equator and poles) is decreased.  But global weather is driven primarily by that gradient: when the meridional temperature gradient is large, polar air is colder relative to equatorial air, so the pole-to-equator density contrast of Earth-surface air is larger, exerting larger forces to drive dense polar air toward the equator and vice versa.  The cold air sinks and flows equator-ward, the warm air rises and flows pole-ward, and the Coriolis effect diverts these flows into giant circulation patterns, including (at the extreme) cyclones and hurricanes.  A larger temperature contrast between equator and poles causes larger density differences and pumps more energy into these global-scale motions.  More energy in the same mass of air means higher velocities.  In other words, the obvious effect of global warming is to reduce the temperature contrast and cause lower wind speeds.

And of course, we humans injected vastly less CO₂ into the atmosphere in the 50 years from 1900 to 1950 than we did in the following 50 years: therefore AGW must have been much stronger in more recent history.

But so much for how things “ought” to work: Dr. Kelly has (gasp!) actually looked at the data on weather extremes to address this issue.  He found that “the weather in the first half of the 20^th century was, if anything, more extreme than in the second half”.  In other words, the actual quantitative data on weather extremes confirms the common-sense understanding of a decreased meridional temperature gradient and agrees with the consensus of the IPCC, but flatly contradicts the glib prophecies of impending doom of the fear-mongers.  These prophecies, though quantitatively unfounded, have the PR virtue of being frighteningly draconic and easily understood by politicians and policy makers who think and argue qualitatively.  But who gets more attention, the person who says "Tomorrow will be a little better than today", or the one who shouts "Disaster coming!"?

Dr. Kelly concludes, “The lack of public, political and policymaker appreciation of the disconnect between empirical data and theoretical constructs is profoundly worrying, especially in terms of policy advice being given.”

You don’t have to take my word for this.  The original technical publication is available online:

http://www.omicsgroup.org/journals/trends-in-extreme-weather-events-since-1900--an-enduring-conundrum-for-wise-policy-advice-2167-0587-1000155.pdf