The shadow of the black hole at the center of Messier 87 [Image: Event Horizon Telescope collaboration et al.]

2019 was a year of historic firsts – it saw the first landing on the far side of the Moon, a flyby of the most distant Kuiper Belt object yet studied, the first known interstellar comet and an image of a black hole.

First landing on the far side of the Moon
The China National Space Administration (CNSA) set the bar high for 2019. On January 3rd the Chang'e-4 lander successfully set down in the Von Kármán crater on the Moon's far side. The Moon has no permanently dark side, but one side of it never faces Earth. The lander gathered some unusual material that may well have come from the mantle, the layer between the crust and the core of the Moon. Scientists hope it will help to understand better not only the Moon's evolution, but also other terrestrial planets since the Moon's lack of atmosphere leaves the surface relatively undisturbed.

Meteor and eclipsed Moon
A January total eclipse got attention from around the globe. Some observers of totality had a bonus sight in the form of a flash as a bit of space rock hit the lunar surface. This is rare, because a lunar impact flash is usually lost in the brightness of a full moon.

More Saturnian moons
Jupiter, the king of the Solar System, has 79 known moons. However, in 2019 Saturn pulled ahead of it in the moon stakes with the discovery of twenty new ones. The ringed planet now has 82 known moons. Scott Sheppard headed the observing team that discovered the new ones. In 2018 he led a team that found 12 new moons orbiting Jupiter.

Hayabusa 2 lands on Ryugu
The Japanese space agency JAXA launched Hayabusa 2 in 2014, and it rendezvoused with near-Earth asteroid Ryugu in June 2018. The spacecraft went into orbit around the asteroid, surveying it, and twice touched down to collect samples, once in February and once in July. In November 2019 it left for home.

Osiris Rex at Bennu
Hyabusa wasn't alone out among the asteroids. NASA's Osiris Rex was studying the asteroid Bennu. Ryugu and Bennu are thought to be two pieces of the same parent body, which allowed for a useful comparison of data. Bennu is the smallest body which has ever been orbited by a spacecraft, and its weak gravity means that care is needed to maneuver Osiris Rex around it. Bennu is also a potentially hazardous asteroid, so it is of particular interest.

New Horizons visited Arrokoth
On New Year's Day, New Horizons arrived at its target. It's the most distant object ever visited, so far away that it takes 298 years to orbit the Sun. It's made up of two lobes, and probably formed in a gentle collision. When the spacecraft arrived, the body was called Ultima Thule, a name from classical times that we might think of as the Last Outpost. However, later came concerns about Nazi associations, and Ultima Thule became Arrokoth. This word meant “sky” in the language of the native American Powhatan people.

Far FarOut
In December 2018, a team lead by Scott Sheppard discovered the most distant Solar System object yet known. It's 120 times farther from the Sun than Earth. They nicknamed the new object Farout. One snowy day in February 2019 Sheppard was looking through their images of the outer Solar System when he found something 140 times more distant from the Sun than Earth is. It's been nicknamed FarFarOut.

Super-puff exoplanets
Many of the exoplanets so far discovered are analogous to Solar System bodies. However, we don't have anything remotely like the super-puff planets. They've been known since 2014, but in 2019 researchers released the results of a study using Hubble Space Telescope data. The super-puff planets are young gas giants almost the size of Jupiter, but with only 1/100th of the mass. This gives them the density of cotton candy. Three such planets orbit the sunlike star Kepler-51.

An interstellar comet
In 2017 the first known interstellar visitor came whizzing through the Solar System. At first it was identified as a comet, but eventually not classified as one. In 2019, however, another object not bound to the Sun came along. It was first reported by telescope maker and amateur astronomer Gennady Vladimirovich Borisov, and has been designated Comet 2I/Borisov.

First ever image of a black hole
The aim: Image a black hole 6.5 billion times more massive than the Sun. It lies about 55 million light years away at the center of galaxy Messier 87. The means to accomplish the aim was the Event Horizon Telescope (EHT). This was composed of eight radio observatories located across four continents. They collected data over a ten-day period in April 2017, and two years of computer analysis was then needed to produce the image from the data. We can't see the black hole itself because light can't escape from it. We see its shadow and the bright ring formed as light is bent in the intense gravity. An amazing achievement.