Bakersfield Night Sky – September 17, 2016
By Nick Strobel
Last week was a good week for solar system exploration. Earlier in the week, the Rosetta spacecraft orbiting Comet 67P/Churyumov-Gerasimenko finally located the Philae lander, less than 30 days before the Rosetta mission ends on September 30. Back in mid-November 2014, the Philae lander became the first craft to land on a comet. Unfortunately, the landing system designed to latch onto the comet did not work and Philae bounced a couple of times in the extremely weak gravity of the comet before it settled in a deeply shadowed crevice. Cut off from the sunlight needed to power its instruments, Philae did what research it could do on battery power alone. The battery ran out 57 hours after landing.
A number of excellent results were sent to the Rosetta orbiter in those 57 hours and the Rosetta orbiter has been very productive in the following almost two years. One of the surprises found by Rosetta is the wide variety of surface structures—nineteen on just the northern part of the comet alone. There is a layer of organics along with over a hundred water ice patches on the surface. Large cliffs several hundred meters high and pits up to 200 meters deep are the sources of the dust jets.
One of the key findings of Rosetta is that the water on the comet is very different than the water in our oceans. The comet has three times greater proportion of deuterium in its water molecules than what we have on Earth. One of the ideas of where Earth’s water came from is millions of comet impacts in its early history as it swept up material from the then crowded solar system. Though some comets have similar deuterium proportions to the Earth’s water, most comets do not.
Putting the water data together with the proportions of other compounds found on 67P, it looks like this comet was made of the cold components of an interstellar cloud instead of the warmer solar nebula from which the sun and planets formed. Using radio waves through the comet from Philae to Rosetta, we found out that the “head” piece of the double-lobed comet is very porous—about 75% to 85%, so it is essentially a rubble pile of dust and ices. The pit walls have bumps that are probably the original building blocks of the comet that accumulated 4.6 billion years ago.
Three days before Philae was found NASA released results from Juno’s first close flyby of Jupiter. The views of Jupiter’s north pole show that the polar regions are unlike anything seen on other planets. Jupiter’s north pole is much bluer than the regions closer to the equator we can see from Earth and there are none of the horizontal belts and zones. The hexagonal cyclones we see at Saturn’s poles are not found on Jupiter’s poles.
Juno’s infrared camera was able to image Jupiter’s southern aurora. That is something we cannot do from Earth or its vicinity, including the Hubble Space Telescope. The Radio/Plasma Wave Experiment on Juno recorded the emissions from the aurorae at both poles. The Juno team converted the radio emission into audio and into a sonogram (like a voiceprint). Go to the Juno site at www.nasa.gov/juno to hear the ghostly sounds of Jupiter’s aurorae.
On September 8, the OSIRIS-REx (short for “Origins Spectral Interpretation Resource Identification Security - Regolith Explorer”) launched for a rendezvous with the small Near-Earth Object Bennu in 2018. In July 2020, OSIRIS-REx will attempt to collect up to two kilograms of Bennu’s material and return it to Earth in September 2024.
Bennu was chosen because it has an orbit similar to Earth, making a sample-return mission possible and it is large enough (about 500 meters diameter) that it does not spin so rapidly to fling off surface material and damage the spacecraft. Furthermore, Bennu is a carbon-rich asteroid containing organic molecules, volatiles, and amino acids from the beginning of the solar system.
All those reasons and also because Bennu comes very close to the Earth every six years and there is a 0.037% chance it will hit the Earth in the late 22nd century. OSIRIS-REx will test out the “gravity-tractor” method of changing Bennu’s path through the weak gravity pull of the spacecraft. In the late 22nd century, Bruce Willis won’t be around to blast the asteroid to smithereens, so we’ll need a gentler way to coax Bennu into not hitting the Earth.
Autumn officially begins at the equinox September 22 at 6:21 a.m. Pacific time when the sun crosses the celestial equator heading southward. The following day tickets go on sale for the Mars Travel Guide and the Earthquake shows at the William M Thomas Planetarium.
The attached chart below shows you where to look for Venus shortly after sunset and Mars and Saturn at 9 p.m. Venus will continue to climb up higher in the western sky after sunset over the following months. Jupiter is now essentially lost in the glare of the setting sun. On September 26 Jupiter will go behind the sun as seen from our terrestrial vantage point. In the later evening sky, the triangle formed by Saturn, Antares, and Mars continues to lengthen as Mars scoots across the sky toward Sagittarius.
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