Bakersfield Night Sky — May 6, 2017
by Nick Strobel
The Saturn-orbiter, Cassini, made its first pass through the narrow gap between the rings and Saturn’s cloud tops in great shape on April 26. At just 1900 miles from the cloud tops, Cassini whizzed through the gap at 77,000 mph relative to Saturn. Cassini oriented itself so that its large radio communication dish was in front to act as a shield against any larger than smoke-sized particles that might be in the gap. Later it turned itself to point the dish toward home to tell us it was okay and send back amazing pictures and other data.
The second pass of a total 22 dives happened on Tuesday, May 2. However, that is still in the future as I prepare this column for the Saturday publish date. I hope Cassini made it through safely! All it takes is one tiny sand-grain particle to hit Cassini in the wrong place to permanently disable the craft. Even if the spacecraft gets disabled, the orbits are now pre-destined to end in mid-September when Cassini plunges into Saturn. Future passes in May will happen on May 9, 15, 22, and 28. See saturn.jpl.nasa.gov for the latest pictures and data from the other instruments.
A couple of weeks ago a team from the MEarth Project announced the best exoplanet for follow-up observations of its habitability, better than Proxima Centauri b (the closest one to us) and TRAPPIST-1 (the one with between 3 and 7 habitable worlds). This latest discovery is a “super-Earth” orbiting a cool red star called “LHS 1140” 41 light years away. Although, LHS 1140 is not as close as Proxima Centauri b and TRAPPIST-1, LHS 1140 appears to be not as active as them, increasing the chance that the exoplanet might still have a decent-sized atmosphere.
M-type stars can produce flares with thousands of times the energy of our sun’s flares and large amounts of nasty X-rays. All that radiation can whittle away a nearby planet’s atmosphere to nothing and wipe out life on the exoplanet’s surface. Proxima Centauri appears to be fairly active and TRAPPIST-1 might also be that way because it rotates quickly. LHS 1140 is much quieter and does not emit much harmful X-ray light.
The common small red stars are called “M-type” stars by astronomers (see chapter 11 of my Astronomy Notes website for why) and they are the most common type of star in the universe. The MEarth Project looks for Earth-sized planets orbiting the nearby M-type stars by looking for tell-tale dips in the cool star’s brightness as the planet crosses in front of it. The amount of the dip depends on the size of the exoplanet. LHS 1140b is about 40 percent larger than Earth with about 6.6 times the Earth’s mass. The size and mass enable us to calculate its density. LHS 1140b is most certainly a rock-metal world. It orbits its star once every 25 days and receives about half as much starlight from its star as we get from the sun.
Besides being more likely to have retained its atmosphere than Proxima Centauri b and the TRAPPIST-1 exoplanets, there are two other advantages LHS 1140b has over the others. The first is that it passes in front of (“transits”) a quiet star, so starlight filtering through the planet’s atmosphere would have imprints of what’s in the planet’s atmosphere. We can check for things like water, carbon dioxide, and oxygen. Proxima Centauri b does not transit its star, so no spectroscopy of its atmosphere is possible. Also, we cannot directly measure Proxima Centauri b’s size. We only know its mass.
Although the TRAPPIST-1 exoplanets transit their star, the more energetic activity of TRAPPIST-1 will make spectroscopy of the exoplanet atmospheres harder to do. The James Webb Space Telescope and future mega ground-based telescopes like the Giant Magellan Telescope will be needed to do the spectroscopy. The second advantage of LHS 1140b is that its density is high enough to be a rock-metal world like the Earth. Only one of TRAPPIST-1’s exoplanets has had its density measured accurately and it’s too low to be rocky. Maybe the other TRAPPIST-1 exoplanets are the same way.
Tonight, May 6, is the first of the KAS public star parties at Panorama Park for 2017. From sunset to about 10 PM, the Kern Astronomical Society will be hosting a free star party for anyone to look through their telescopes. The waxing gibbous moon will be one target as well as bright Jupiter to the lower left of the moon. The KAS telescopes are powerful enough to see the bands on Jupiter as well as the four Galilean moons. To the east of Jupiter will be Callisto (furthest out from Jupiter) and Europa (the one with deep ocean of water below its icy surface). To the west of Jupiter will be Io (the one with many active volcanoes) and Ganymede (largest moon in the solar system, larger than Mercury). Another nice target will be the globular cluster, M13, in Hercules. Come take a look! See the attached star chart below.
The Moon will be a waning gibbous on the night of BC’s commencement. It will rise after the conclusion of the ceremony, so the sky will be dark for the fireworks show at the end. (Well, as dark as a Bakersfield sky can be anyway.)
Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com