Bakersfield Night Sky – April 2, 2016
By Nick Strobel
Jupiter is now shining brighter than any star in our night sky halfway up in the east by the time when evening twilight ends. Last week I tuned into a webinar about the Juno mission to Jupiter that will arrive at Jupiter on July 4th. Besides the huge amount of science they'll learn about Jupiter and what it can reveal about our origins, I was also impressed by the cleverness and creativity of the engineering that went into designing the instruments and the analytical techniques that will go into interpreting the data that comes streaming back to us. It makes me believe that we have the ability, the know-how, to figure out how to solve all of the big problems facing us today if we put our minds to it instead of denying that the problems exist.
At about midnight, Mars should be high enough to see easily in the southeast at the head of the scorpion, Scorpius (see the first chart below). Last week, scientists released a gravity map of Mars. The map is the result of 16 years of ultra-precise measurements of the motions of three different orbiters. The gravity map enables us to probe the interior structure of the planet. The gravity field map data show that the outermost edge of Mars's iron core is still molten. The part of the core that is still molten is probably too thin to generate a global magnetic field.
That lack of a global magnetic field leaves the atmosphere unprotected from the battering of the solar wind, the million mile per hour stream of charged particles constantly flowing out from the Sun. Over millions of years, the solar wind has blasted away the atmosphere of Mars so the air pressure at the surface is just 1% that of the Earth's air pressure. The martian surface air pressure is equivalent to the very low air pressure you'd feel at an altitude of 100,000 feet on Earth: too low for us to survive and too low for liquid water to remain on the surface.
The scientists were also able to measure from the gravity map how much of the carbon dioxide atmosphere freezes out in the winter as dry ice at the polar ice caps. About 3 trillion tons of carbon dioxide or 12% of the atmosphere freezes out in the northern hemisphere winter and 4 trillion tons or 16% of the atmosphere freezes out in southern hemisphere winter. The seasons in the southern hemisphere are more extreme than in the northern hemisphere because Mars's orbit is more elliptical and it is at aphelion (furthest from the Sun) during the southern hemisphere's winter. This means that the summers in the south are short and hot and the winters long and cold while the northern hemisphere seasons are more temperate.
About 45 minutes behind Mars is Saturn between Scorpius and Ophiuchus. The rings are still favorably tipped toward us to get a nice view through a telescope. A recent news story about the rings noted that the rings have not always been there. Astrophysics dynamicists (those who study the motions of objects acting under the force of gravity) have known for a long time that the rings of the planets are transient due to the gravity interactions of the ring particles with each other and the pressure of sunlight. What is the new is that we may have figured out when the rings formed: just 100 million years ago, or about when the dinosaurs were looking around for a tasty mammal to eat. Furthermore, it looks like from the computer models that moons inside of Titan's orbit (Dione, Rhea, Mimas, Tethys, Enceladus, and numerous tiny ones) were formed at that time as well from the debris left from collisions of an earlier generation of moons. I wonder what the rings will look like 100 million years from now (if they're even still around).
Two-and-a-half hours behind Saturn is dwarf planet Pluto, near the handle of the Teapot part of Sagittarius. We continue to get surprising results back from the New Horizons spacecraft. The latest surprise is features that look like liquid once flowed on its surface when its atmosphere was thicker and warmer. However, the liquid would not have been water but something much colder: liquid nitrogen. How long ago the liquid nitrogen existed is not known. We see a frozen lake and channels. Pluto clearly shows that even dwarf planets can have a mighty interesting geological past!
Speaking of dwarf planets (I'm glad you asked), the Dawn spacecraft is now in its lowest orbit around Ceres and is returning great data. The spacecraft is now close enough for all of the instruments that measure composition to get data, including the neutron and gamma-ray counter. The data show that the sub-surface water ice is present closer to the surface at the poles than at lower latitudes.
The two bright spots on Ceres are now revealed to be multiple spots and the largest and brightest spot is a geologic dome with many fractures crisscrossing the top and flanks of the dome. We still don't know for sure of what the bright material is made. The Dawn team continues to take votes on what the bright spots could be (volcano, geyser, salt deposit, water ice, etc.) at www.jpl.nasa.gov/dawn/world_ceres/ .
Those who don't like to stay up late can try to pick out Mercury low in the west just after sunset. It is heading towards its best appearance for 2016 in mid-April. On April 8th a very thin Waxing Crescent Moon will be just to the left of bright Mercury (see the second chart below).
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