2019 in space: 25 notable missions from the last year

On Jan. 1, NASA's New Horizons probe flew past the most distant solar system object yet visited: the small icy world Arrokoth in the Kuiper belt, 4 billion miles from the sun. Formerly known as 2014 MU69, the object resembles two red-colored squashed spheres stuck together. Arrokoth means "sky" in the Powhatan/Algonquian language and is only about 22 miles long and 6 miles thick.

The Chinese Lunar Exploration Program probe Chang'e-4 (for the moon goddess in Chinese mythology) landed on the moon's far side on Jan. 3, the first craft to ever accomplish such a landing. The lander deployed a rover named Yutu-2, which has identified rocks that formed deep under the moon's surface. The moon's far side, which never faces Earth, is very different from the side seen from Earth, and signals from far-side moon missions require using relay satellites since they can't communicate directly with the ground.

Long-duration gamma-ray bursts (GRBs) are the explosions of stars significantly larger than the sun, and as such, are some of the brightest events in the cosmos. NASA's Neil Gehrels Swift Observatory, which was built to monitor these explosions, spotted the most energetic burst ever seen in January. The gamma-ray light emitted by GRB 190114C had roughly 10 times more energy than any other GRB ever seen. This means the material emitting the light was moving at 99.999% of the speed of light.

This year marked the end of one of NASA's most successful missions, the Mars Exploration Rovers, when the Opportunity rover failed to wake up from hibernation following a dust storm on Mars. Designed to operate for 90 Martian days and travel just 1 kilometer, Opportunity lasted for 15 years and traveled 45 kilometers. During its long scientific life, it uncovered evidence for Mars' watery past in the form of minerals that form in wet conditions.

After the retirement of the Space Shuttle in 2011, NASA has commissioned the development of new capsules for use by astronauts to get to the International Space Station (ISS). One of these, the Crew Dragon from the private company SpaceX, successfully completed an uncrewed test docking with the ISS on March 3 and returned to Earth on March 8. Unfortunately, a later test of this capsule failed catastrophically, and further tests without humans are continuing before any astronauts can be safely trusted to the equipment.

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NASA's OSIRIS-REx spacecraft arrived at asteroid Bennu last year, and since early this year has been hunting for a place to sample the material on the surface before returning to Earth. Just one problem: Bennu's surface is much rockier than expected, meaning it's been difficult to find a safe place to use the spacecraft's sampling arm. Meanwhile, OSIRIS-REx has revealed active plumes of material jetting from the asteroid's surface, which is a fun mystery for scientists to solve.

Landing on other worlds is hard, as evidenced by the crash of Israel's first moon probe Beresheet on April 11, when its engine suffered a minor problem that escalated upon its final approach to the moon. Beresheet (meaning "in the beginning" in Hebrew) was funded privately by the nonprofit SpaceIL and the company Israel Aerospace Industries. Israel is already planning the next attempt, following other historical space programs that had to try more than once before succeeding.

One of the candidates to ferry astronauts to and from orbit is the reusable New Shepard rocket from the private spaceflight company Blue Origin. Blue Origin successfully tested New Shepard without a human crew three times this year, in January, May, and December. The tests are in preparation for flights involving astronauts and "space tourists" in the future. The May and December test launches also carried art projects and dozens of science experiments designed by university researchers to study various conditions in microgravity. The Dec. 11 test marked the 12th of its kind for Blue Origin's reusable rocket.

On May 23, SpaceX launched the first 60 Starlink satellites designed to provide global internet access, followed by a second launch on Nov. 11. The high visibility of these satellites to astronomers has raised concerns around the world since SpaceX and other companies plan to launch thousands eventually. This has the potential to complicate astronomical surveys, including those dedicated to the early detection of asteroids.

NASA's Juno spacecraft has been orbiting Jupiter since 2016, mapping the giant planet's gravity and magnetic field to understand its mysterious interior. This year, Juno provided the first data on how Jupiter's magnetic field changes over time, the first such measurements for any planet other than Earth. These fluctuations indicate that the magnetic field may be driven by fast-moving particles deep inside Jupiter.

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The Japanese Aerospace Exploration Agency (JAXA) spacecraft Hayabusa2 touched down twice—on Feb. 21 and July 11—on the surface of the near-Earth asteroid Ryugu. These touchdowns involved firing a projectile into the asteroid's surface and collecting the material ejected for study. Ryugu and other asteroids provide a glimpse of the early solar system and insight into how these objects could potentially be steered away if they pose a threat to Earth.

The Indian Space Research Organization (ISRO) launched Chandrayaan-2, its second moon orbiter spacecraft, on July 22. The spacecraft also carried a lander and robotic rover, which unfortunately crashed on the surface of the moon's far side. However, the orbiter itself is operating successfully, following the original Chandrayaan spacecraft.

What the Hubble Space Telescope does for visible light astronomy, NASA's Chandra X-ray Observatory does for X-ray astronomy. Since 1999, Chandra has provided a wealth of knowledge about galaxies, black holes, the remnants of supernovas, galaxy clusters, and many other high-energy astronomical phenomena. This year marks the 20th anniversary of the launch of both Chandra and ESA's X-ray telescope XMM-Newton.

ESA's Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) consists of two satellites flying in the same orbit around Earth. Because gravity is stronger in some places than others, thanks to the density of rock or even ice, the two satellites speed up or slow down relative to each other, allowing for precision measurement. The lasers carried by the GRACE-FO can measure the separation to an accuracy of roughly the width of a single atom, providing a demonstration of the technology that will eventually be used in next-generation gravitational wave experiments.

Named for the ancient Greek goddess of the moon, NASA's Artemis Project is an ambitious program to land astronauts on the moon in the next decade. The program involves the Space Launch System (SLS) rocket and Orion capsule, currently under development. Artemis was announced in July, but many experts have expressed doubt about the short timeline and lack of funding necessary to successfully send the first people to the moon since the Apollo program ended in the 1970s.

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Most known exoplanets—planets in other solar systems—orbit small, red stars, which are stormier than Earth's sun. NASA's Spitzer Space Telescope observed the infrared spectrum for the rocky exoplanet 55 Cancri e and determined it probably doesn't have an atmosphere. This confirms that stellar storms from red stars might strip the atmosphere from their planets, lowering the chances for habitability on many of these worlds.

Fires in the Brazilian Amazon basin have been especially concerning this year, a situation not helped by the current nationalistic government of the South American nation. Scientists and humanitarians monitoring the situation rely on Earth-observation satellites, such as NASA's Terra and Aqua observatories. The thermal monitors on these satellites help identify the location and severity of fires, comparing them to past burn patterns.

We've known for a long time that cities are hotter than surrounding rural areas, known as the "urban heat island effect." A 2019 study using data from NASA/U.S. Geological Survey's Landsat 8 showed that poor neighborhoods in American cities with histories of discriminatory housing practice—segregation and redlining—are even hotter. This study was made possible by Landsat 8's thermal capabilities, which are sufficiently high resolution to distinguish between neighborhoods in a single city.

NASA's Transiting Exoplanet Survey Satellite (TESS) is designed to find exoplanets, but because it scans the sky for fluctuations in light, it is also well-suited for spotting rare events—like a black hole destroying a star. The very distant black hole is roughly 6 million times the mass of the sun, and TESS captured the light produced when it tore a star apart in unprecedented detail. This data will help astronomers understand how these so-called tidal disruption events happen, which are all the more important because they are very rare.

On Oct. 18, two American women astronauts performed a seven-hour spacewalk to do necessary maintenance on the International Space Station. In doing so, Christina Koch and Jessica Meir were the first all-female spacewalk in the history of spaceflight.

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Last year, the long-running Voyager 2 space probe joined its sibling Voyager 1 in crossing into interstellar space. Scientists used the still-functioning instruments aboard the spacecraft to study this region in new detail, discovering that the sun's magnetic field protects the solar system from 70% of the radiation from dying stars. Both Voyagers also determined that the transitional region between the solar system and interstellar space beyond is much wider and more complex than previously thought.

NASA's InSight lander was partly built to dig deep into the surface of Mars to measure temperature and seismic behavior underground. However, the digger ran into problems when the soil didn't cooperate, leaving the probe—nicknamed the "mole"—stuck. The lander's team back on Earth has continued to work to free the mole, allowing it to dig further in and measure properties like wind speed and surface vibrations.

The thin atmosphere on Mars is mostly carbon dioxide, but scientists have detected tiny traces of other gases, including methane and oxygen. NASA's Curiosity rover measured seasonal atmospheric fluctuations over its entire time on Mars and found more oxygen than expected during certain seasons and less during others for mysterious reasons. On Earth, the abundance of oxygen and methane is tied to living things, but on Mars, another non-living explanation is probably correct—scientists just don't know what it is yet.

NASA's Parker Solar Probe was built to fly through the sun's extremely hot atmosphere, which is the source of the high-energy charged particles known as the solar wind. The first results from Parker, released in December 2019, reveal new complexities in both the sun's magnetic field and the generation of the solar wind. Meanwhile, Parker continues to orbit closer to the sun and will continue to provide new details about the behavior of Earth's home star.

When planets cross in front of their host stars, they block some of that star's light. Astronomers have used this fact to identify thousands of exoplanets. The new CHEOPS (CHaracterising ExOPlanet Satellite) space telescope is a joint project of ESA and Switzerland. It was designed to use that effect to measure the size of exoplanets. CHEOPS was launched on Dec. 17 and will focus on characterizing planets of different sizes.

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