The nearest images of the Sun obtained to date have revealed a new phenomenon, dubbed campfires, which appear as small, bright flickers of light all over the Sun's surface. The Solar Orbiter, a European Space Agency spacecraft launched in February 2020, captured the images from a distance of 77 million km (48 million mi), or about half the distance between Earth and the Sun. The Solar Orbiter will gather vastly more and better observations of campfires as the probe's mission continues for at least the next seven years, with a flight path that will ultimately take the probe to a distance of less than 0.3 astronomical units from the Sun, reaching inside the orbit of Mercury. [An astronomical unit is the average Sun–Earth distance of about 150 million km (93 million mi)]. See also: Astronomical unit

After 13 years studying Saturn and its moons, the Cassini spacecraft’s mission ended on September 15, 2017. Operators at NASA intentionally directed Cassini to plunge into Saturn’s atmosphere, destroying the spacecraft before its fuel supply ran out and the ability to control the probe’s path was lost. Mission planners made this decision to protect against Cassini possibly crashing into Saturn’s moons Titan and Enceladus, which were discovered during the mission to possess environments that could potentially support alien life. See also: Planet; Saturn; Solar system; Space probe

Dawn, a pioneering mission to our solar system's asteroid belt, has gone silent. In late October 2018, Dawn ran out of hydrazine, the thruster fuel needed to orient the spacecraft for communication with Earth and the generation of solar power. Although now retired, the Dawn mission leaves a rich scientific legacy. It is the first and only spacecraft to have visited the dwarf planet Ceres—the largest object in the asteroid belt between Mars and Jupiter—as well as Vesta, the second-largest object in the belt. Before Dawn's arrivals, humanity had little clue as to what these worlds really looked like. See also: Asteroid; Ceres; Earth; Dawn mission; Hydrazine; Jupiter; Mars; Planet; Solar cell; Solar system; Space communications; Vesta

NASA's Curiosity rover has produced new key evidence in determining whether Mars has ever hosted life. While drilling in an ancient lakebed, Curiosity recently discovered organic material more complex and abundant than previously found on the Red Planet. On Earth, chains of organic molecules, which contain the element carbon, form the basic building blocks of life. Far more investigation will be necessary, however, to identify the source of the Martian material as either biological or geological. Besides life, likelier sources of the organic material include impacting asteroids and volcanism. See also: Asteroid; Astrobiology; Carbon; Geology; Mars; Organic chemistry; Volcano

Researchers recently announced the discovery of the farthest object ever identified within our solar system. Designated 2018 VG18 and nicknamed Farout, the object is located about 120 astronomical units (AU) from the Sun, or 120 times the average Sun-Earth distance. For comparison, the second most-distant object known in our solar system, Eris, orbits the Sun at a distance of 96 AU, while Pluto's approximate distance is 34 AU. Like those other two bodies, Farout is likely a dwarf planet, with a diameter of about 500 km (311 mi), suggesting it possesses enough mass to have assumed a spherical shape under the force of gravity. See also: Astronomical unit; Astronomy; Gravity; Mass; Planet; Pluto; Solar system; Sun

The ice-covered moon Europa has long intrigued researchers as a potential abode for extraterrestrial life. Although its orbit around Jupiter is frigidly far from the Sun, Europa harbors an internal ocean. Furthermore, this inner liquid reservoir likely receives warming energy due to gravitational interactions amongst Jupiter and its numerous moons. Understandably keen to study Europa's innards, scientists have pinned their hopes on a future robotic lander that might drill through the moon's frozen shell. New findings from an old spacecraft, however, have strongly indicated that plumes of material can escape from Europa's inner ocean into space, offering a far simpler way to learn Europa's secrets. See also: Gravity; Jupiter; Ocean; Sun

The ExoMars orbiter has detected a green glow emanating from excited oxygen molecules in the dayside atmosphere of Mars. The observations, gathered over a six-month period last year, confirm a four-decades-old prediction and represent the first time anyone has documented this phenomenon on a planet besides Earth. Further study of this green glow will help scientists better understand the mechanisms behind how a similar glow is generated in Earth's atmosphere, as well as the composition and dynamics of the Martian atmosphere. See also: Atmosphere; Earth; Mars; Planet

The third mission ever to visit the solar system's innermost planet, Mercury, began on October 20, 2018, with the launch of BepiColombo. The mission will attempt to answer longstanding mysteries about Mercury, including its internal structure and interactions with the stream of charged particles streaming off the Sun, known as the solar wind. See also: Mercury (planet); Planet; Solar system; Solar wind; Sun

The Kepler space telescope—the most prolific discoverer of exoplanets, or worlds outside our solar system, to date—has run out of fuel and ceased science operations, NASA announced on October 30, 2018. Kepler leaves a legacy for first revealing that exoplanets are ubiquitous, actually outnumbering stars. Within the Milky Way Galaxy alone, home to some 300 billion stars, Kepler's findings have statistically suggested that there are on the order of a trillion planets. See also: Exoplanet; Galaxy; Kepler mission; Milky Way Galaxy; Planet; Solar system; Star; Telescope; Universe

The science of exoplanets—worlds beyond our solar system—has thus far focused more on quantity than quality. The considerable distances to most of the several thousand exoplanets catalogued to date, coupled with the limitations of current telescope technology, mean that astronomers know little about these alien worlds’ properties beyond the broad strokes of size, mass, and temperature. An exception to this generality is a hot, Saturn-mass planet designated WASP-39b. In a recent study, new observations of WASP-39b from the Hubble Space Telescope, combined with data from the Spitzer Space Telescope and the ground-based Very Large Telescope, have together painted the most comprehensive portrait yet of an exoplanet’s atmosphere. See also: Atmosphere; Exoplanet; Hubble Space Telescope; Saturn; Spitzer Space Telescope; Telescope; Very Large Telescope