The year 2017 was an exciting one for astronomy, full of interesting events and discoveries. It was hard to choose only ten, but here is my selection.
Star system with 7 Earth-sized planets
We learned that the ultra-cool dwarf star TRAPPIST-1, 40 light years away in Aquarius, has at least seven Earth-sized planets. Three of the outer ones are in the star's habitable zone, and Hubble Space Telescope evidence suggests that there could be substantial quantities of water on the outer planets.
Kepler-90 vs The Sun: 8 all
Like the Sun, Kepler-90 is a G-type star, but somewhat more massive, hotter, and much younger than our star. It's about 2500 light years away in the constellation Draco, and was known to have seven planets. Now, with the discovery of planet Kepler-90i, we know our Solar System has an equal in terms of known planet numbers. However all of the Kepler-90 planets are closer to their star than Earth is to the Sun. An interesting aspect of the discovery is that it was made by exploring Kepler mission data using a type of machine learning.
First confirmed interstellar visitor
In October, a new object was spotted at Haleakala Observatory in Hawaii. Whizzing through the Solar System, it was first identified as a comet, and then an asteroid. Unusually, it was long and thin, dark red, and tumbling, not rotating. Whether comet or asteroid, further observation showed it couldn't have originated in the Solar System because it was moving too fast to be orbiting the Sun. This first known interstellar object was designated 1I/2017 U1, and named ‘Oumuamua, meaning first scout in Hawaiian. (What looks like an apostrophe is part of the name.)
Dwarf planet with rings
The dwarf planet Haumea was discovered to have a ring system. Although there are two known ringed asteroids, Haumea is the first object beyond Neptune found to have a ring.
North American total eclipse
North Americans were treated to a fantastic solar eclipse during the summer. A band of totality went from coast to coast, and varying degrees of partial eclipse covered the rest of the continent. Besides delighting the public, eclipses are useful to scientists. They can, for example, be used to study the Moon's orbit, carry out cosmic-ray counts, or observe Mercury.
First white dwarf pulsar
The first pulsar was discovered in 1967 by Jocelyn Bell Burnell. Pulsars are rapidly spinning neutron stars with high speed jets streaming out of the magnetic poles. If a jet points in our direction when the star spins, we see it as a pulse. (It's often compared to a lighthouse.) Although some people had thought a white dwarf could also become a pulsar, no one had ever found one. Until 2017. AR Sco, a white dwarf 380 light years away in the constellation Scorpius, zaps its neighboring star with powerful beams.
Life on Enceladus and Ceres?
There isn't any evidence for life on either Saturn's moon Enceladus or dwarf planet Ceres. However both places have promise. The Cassini spacecraft detected molecular hydrogen (H2) in a flyby of Enceladus. A study published in the journal Science suggests it could be the result of the kind of chemical reactions associated with life in deep-sea hydrothermal vents in Earth's oceans. And NASA's Dawn mission found evidence for organic material on Ceres. Organic molecules are necessary, though not sufficient, components of life on Earth.
Cassini's Grand Finale
On September 15, the Cassini spacecraft ended its 13-year exploration of the Saturnian system by plunging into Saturn. Before the final plunge the Grand Finale mission included 22 dives between Saturn and its rings. This would have been foolhardy earlier in the mission because of the risks involved, but it worked, and Cassini collected unprecedented close-up data.
Most distant quasar yet discovered
A quasar is the heart of an extremely bright galaxy, powered by a supermassive black hole. Quasars are too far away to work out their distances in light years. However astronomers can measure their redshift, i.e., how much the wavelength of their light is stretched by the expansion of the Universe as they travel to Earth. Higher redshifts mean greater distances, which also means you're looking back farther in time. In 2017 a quasar was discovered at redshift 7.54. This is the highest redshift for any quasar yet discovered, the light having taken over 13 billion years to get to Earth. The Universe – now 13.8 billion years old – was only 600,000 years old when the light began its journey.
More advances in gravity wave astronomy
In 2016 the upgraded observatory of the LIGO Scientific Consortium detected gravity waves produced by two black holes colliding. It was an outstanding achievement, and the 2017 Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish for their part in the work. In 2017 three more detections followed, including one resulting from the merger of two neutron stars. For the first time, the VIRGO detector in Italy joined in with the LIGO detectors in Washington and Louisiana. This greatly improved the accuracy of pinpointing the location of an event.