by Kim Malville
August is the very best month of the year for us in the northern hemisphere to spot meteors. Beloved by campers in the summer, it is a time for sleeping outside without a tent. The Perseids begin to appear in late July and reach their peak on August 12. If you watch the trajectory of the meteor and can trace it backward, if it is a Perseid, it would have originated near the constellation of Perseus toward the northeast.
August 11, 12 – The Perseids produce up to 60 meteors per hour at their height. It is produced by comet Swift-Tuttle, which was discovered in 1862 and as it orbits the sun the comet drops tiny particles along its orbit. The Perseids are famous for producing a large number of bright meteors. The shower runs annually from July 17 to August 24. The waxing gibbous moon will set shortly after midnight, leaving the perfect night sky for an excellent early morning show of fireworks without the noise. Find a comfortable chair and face northeast. Although these meteors radiate from Perseus, they can appear anywhere in the sky.
August 16 – Mercury reaches its greatest distance from the sun as seen from the earth. This is the best time to view Mercury since it will be at its highest point above the horizon in the evening sky. Look for the planet low in the western sky just after sunset.
August 18 – This full moon was known by early Native American tribes as the Full Sturgeon Moon because the large sturgeon fish of the Great Lakes and other major lakes were more easily caught at this time of year. This moon has also been known as the Green Corn Moon and the Grain Moon.
August 27 – Conjunction of Venus and Jupiter. A spectacular conjunction of Venus and Jupiter will be visible in the evening sky. The two bright planets will be extremely close, appearing only 0.06 degrees apart. Look for this impressive pairing in the western sky just after sunset.
Juno reaches Jupiter
The spacecraft Juno completed a five-year cruise to Jupiter, arriving in Jupiter’s magnetosphere on July 4, 2016. The spacecraft traveled over a total distance of roughly 1.74 billion miles to reach Jupiter. The spacecraft will orbit Jupiter 37 times over the course of 20 months.
Juno’s highly elliptical polar orbits take it close to the planet—within 2,700 miles above its cloud tops. Each of these lower orbits takes 14 days and the spacecraft is expected to complete 37 orbits until the end of the mission. One of the most fascinating goals of the mission is to learn about Jupiter’s core. At present it is believed to have a rocky core surrounded by a thick sheath of liquid hydrogen, which behaves like a conducting metal in which electrons are free to move. This huge planet spins on its axis every 9 hours and 50 minutes. That rapid spin generates a magnetic field, the strongest of any planet’s, some 14 times stronger that of the earth. The magnetic field results in intense trapped particles, like those of our Van Allen belts, and brilliant auroral displays at its pole, such as are visible in the figure.
Juno is scheduled to reach the end of the mission during its 37th orbit and perform a controlled deorbit and disintegrate into Jupiter’s atmosphere. During the mission, the spacecraft will be exposed to high levels of radiation from Jupiter’s Van Allen belts, which may cause future failure and risk collision with Jupiter’s moons. The controlled deorbit will eliminate space debris and risks of contamination. Because of the high velocity collision of the spacecraft and the dense atmosphere, Juno will burn up and disintegrate. NASA is currently formulating a mission to explore Europa and investigate whether the icy moon might be habitable. If a fragment of disintegrating Juno were to land accidentally on Europa and inadvertently contaminate part of its surface with organic material from Earth that would certainly mess up our future search for indigenous life. Thus, suicide was built into the mission plans.
Life on Europa
A new NASA study suggests that the necessary balance of chemical energy for life could exist on Europa. The moon is believed to hide a deep ocean of salty liquid water beneath its cracked icy shell. Whether the Jovian moon has the raw materials and chemical energy in the right proportions to support biology is a topic of great interest.
The study compared Europa’s potential for producing hydrogen and oxygen with that of Earth, through processes that do not directly involve volcanism. The balance of these two elements is a key indicator of the energy available for life. The study found that the amounts of hydrogen and oxygen should be comparable on both worlds. Cracks in Europa’s seafloor likely open up over time, as the moon’s rocky interior continues to cool following its formation billions of years ago. New cracks in its rocky core would expose fresh rock to seawater, leading to production of more hydrogen, oxygen, and chemical compounds that could nurture life. In Earth’s oceanic crust, such fractures are believed to penetrate to a depth of 3 to 4 miles, while on present-day Europa, water could reach as deep as 15 miles into its rocky interior.
Europa’s rocky neighboring Jovian moon, Io, is the most volcanically active body in the solar system, due to heat produced by the stretching and squeezing effects by Jupiter’s gravity as it orbits the planet. Scientists have long considered it possible that Europa might also have volcanic activity, as well as hydrothermal vents, where mineral-laden hot water would emerge from the sea floor. Like the seafloor vents on earth, these hot vents on Europa could be teeming with life. Deep in its oceans, that life would be protected from deadly radiation from Jupiter’s Van Allen belts. This strange cocktail of water, ice, rock and ionizing radiation may be perfect for creating life.