The Parker Solar Probe approaches the sun in this artist’s depiction. The probe’s path takes it nearer to the sun than any other human-made object, allowing it to make close-up observations of solar activity.
NASA

The Parker Solar Probe has done the unthinkable. It became the first spacecraft to touch the sun! Scientists reported the announcement on Dec. 14, 2021, at the press conference at the 2021 American Geophysical Union Fall Meeting in New Orleans, Louisiana. The probe was built and operated by the Johns Hopkins Applied Physics Laboratory. The probe flew through the upper atmosphere of the sun, called the corona, to collect samples. The samples will allow scientists to understand more about the sun, just like landing on the moon paved the way for scientists to learn about the moon.

The National Aeronautics and Space Administration (NASA) launched the Parker Solar Probe in 2018. The probe completed its first orbit of the sun in 2019. The probe is the fastest human-made object in the solar system. The sun’s gravity is expected to accelerate the probe to extreme speeds of up to 430,000 miles (700,000 kilometers) per hour. Three years after the launch, the probe has arrived at the sun.

The goals of the mission are 1) to study how energy and heat flow through the corona; 2) to gather information on plasma (the gaslike substance the sun is composed of) and magnetic fields near the sun; and 3) to learn more about how high-energy particles travel outward from the sun.

It uses a set of instruments known as FIELDS, which has antennas to measure electric fields and magnetometers to measure magnetic fields. The probe is also equipped with a pair of cameras to capture images of the sun. The probe carries various instruments for studying particles in the solar wind—that is, the continuous flow of particles from the sun.

The sun’s corona can be as hot as 4,000,000 °F (2,200,000 °C). Because of the corona’s low density (concentration of matter), the Parker Solar Probe will not experience the sun’s most intense heat. However, it will encounter temperatures of up to 2,500 °F (1,377 °C)—hotter than lava from a volcano.

The Parker probe is planned to approach the sun 24 times by the mission’s end. Hopefully, the Parker probe can stand the heat and gather more information about the corona and solar winds.

An image of Venus, made with data recorded by Japan’s Akatsuki spacecraft in 2016, shows swirling clouds in the planet’s atmosphere.
Credit: PLANET-C Project Team/JAXA

Venus is heating up—figuratively, that is. It has always been the hottest planet in the solar system, with surface temperatures of about 870 °F (465 °C). But new findings from the mysterious planet have been pouring in. Soon, a new generation of space probes will transform Venus from a sleepy solar system backwater to a bustling hub of scientific discovery.

Venus is the second planet from the sun. It is known as Earth’s “twin” because the two planets are so similar in size. The diameter of Venus is about 7,520 miles (12,100 kilometers). This diameter is about 400 miles (640 kilometers) smaller than that of Earth. No other planet comes nearer to Earth than does Venus. At its closest approach, it is about 23.7 million miles (38.2 million kilometers) away.

But Venus is better described as Earth’s evil twin, in respect to its withering conditions. In addition to the high temperatures, the atmospheric pressure is 90 times greater than that on Earth. Carbon dioxide makes up most of the atmosphere. The skies are strewn with clouds of sulfuric acid.

Scientists sent several probes to learn more about the planet in the 1960’s and 1970’s. But as space agencies learned of its inhospitable conditions, they concentrated their efforts elsewhere, particularly Mars. The last United States National Aeronautics and Space Administration (NASA) mission to study Venus, called Magellan, launched in 1990. Thus, scientists know relatively little about Venus, despite its close proximity to Earth and its similar size.

Despite the dearth of missions in recent years, planetary scientists continue to scan the planet with Earth-based instruments and reanalyze older data. They have returned surprising results.

Last year, a team of scientists announced that they had discovered a gas called phosphine in Venus’s atmosphere. Many living things on Earth produce phosphine; and scientists have not been able to identify any non-biological processes on Venus that might produce it. This raised the possibility that microbial life could exist in Venus’s atmosphere, where the conditions are much milder. But the discovery has been controversial. Other teams have failed to find any phosphine signature.

Last month, a team led by researchers at Queen’s University Belfast left the floating-Venusian-microbes idea high and dry. They found that Venus’s atmosphere does not contain enough water vapor to support life, irrespective of the presence of phosphine. The team determined that even the most extreme microbes on Earth require an environment with dozens of times more water than is available in Venus’s atmosphere.

Another recent study has shed light onto possible changing of Venus’s surface. Previously, Earth was the only rocky planet known to have a moving surface. A team lead by Paul Byrne, a professor at North Carolina State University, found evidence that parts of Venus’s surface might be slowly moving today. Earth’s crust slowly reshapes itself by a process called plate tectonics. Large pieces of the surface, called plates, subduct (sink) under one another, forming mountain ranges and other features. New crust forms along the ridges where the plates pull away from each other. In contrast, Byrne’s team found that pieces of Venus’s crust move like pack ice in polar oceans. Learning more about crust movement on Venus will help scientists understand how such processes develop on other planets, including Earth and exoplanets that might harbor life.

Last month, space agencies announced that not one, but three missions will be exploring Venus in the next 15 years. On June 2, NASA announced it is sending two mission to Venus. The missions were selected as part of part of NASA’s lower-cost Discovery Program. NASA expects to launch both missions between 2028 and 2030.

VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) will orbit the planet and map its surface with greater detail than ever before. It will allow scientists to better understand the planet’s features.

DAVINCI+ (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging) consists of a sphere that will plunge through Venus’s thick atmosphere, studying the atmosphere’s composition. The DAVINCI+ mission planners are seeking evidence of an ocean of water that might have covered Venus’s surface eons ago.

There are other players in the new Venus boom. Last year, American company Rocket Lab announced plans to launch a small probe to Venus as early as 2023. And on June 10, just over a week after NASA’s selection DAVINCI+ and VERITAS, the European Space Agency (ESA) announced that it would also be sending a probe Venus. The EnVision orbiter will search for signs of current and former tectonic activity and the presence of a past ocean. EnVision is scheduled to arrive at Venus in 2034 or 2035.

The desire to learn more about Venus is fed by more than just curiosity about our nearest neighbor. Astronomers are looking for signs of life on exoplanets. But Venus and Earth would look quite similar from light-years away. Learning more about Venus and how it evolved to become so different from Earth will help astronomers better weed out Venus-like exoplanets in their search for ones that are more like Earth.

SpaceX’s Crew Dragon capsule sits atop a Falcon 9 rocket, in preparation for launch on May 27, 2020.
Credit: © SpaceX

A new era of human spaceflight began Saturday, May 30, as Space Exploration Technologies (commonly called SpaceX) launched its Crew Dragon capsule into space. (The launch was originally scheduled for Wednesday, May 27, when it was delayed due to bad weather.) The Dragon became the first private spacecraft ever to take astronauts into orbit. The mission, called the Demo-2 mission, transported National Aeronautics and Space Administration (NASA) astronauts Robert Behnken and Douglas Hurley to the International Space Station (ISS).

Astronauts Bob Behnken (left) and Doug Hurley (right) prepare for the first crewed launch of SpaceX’s Dragon capsule.
Credit: © SpaceX

Millions of people watched from home as SpaceX’s Falcon 9 rocket launched the Dragon from the Cape Canaveral Air Force Station into space. In orbit, the crew tested the spacecraft’s control systems to make sure the capsule was performing as intended before its arrival at the ISS. The Dragon features various modern technologies in its engineering and construction. Unlike previous spacecraft, it has a touchscreen control interface that looks similar to those used in the popular science fiction television series Star Trek.

The International Space Station (ISS)
Credit: NASA

An important part of the mission was docking the Dragon to the ISS. The capsule reached the ISS on Sunday, May 31, about 24 hours after launch. Aboard the space station, Behnken and Hurley will perform research and other tasks with the rest of the ISS crew. They will remain on the ISS for one to four months before undocking the Dragon and re-entering Earth’s atmosphere. The capsule will land in the Atlantic Ocean, where the crew will be retrieved and returned to Cape Canaveral, completing the mission.

If the Demo-2 mission is successful, NASA will certify the Crew Dragon to regularly transport astronauts to the ISS. Since NASA’s space shuttle program ended in 2011, the administration has relied on Russia’s Soyuz spacecraft to transport astronauts to and from the ISS. The Soyuz can transport up to three astronauts at a time, and NASA pays about US $86 million per seat. The Dragon is able to transport up to seven astronauts at once, and the cost per crew member is expected to be around $55 million.

January 8, 2020

Late last year, on Dec. 18, 2019, the European Space Agency (ESA) launched the CHEOPS telescope into space, where it will study the composition of exoplanets. Exoplanets, or extrasolar planets, orbit stars other than our sun. The CHEOPS telescope was launched aboard a Russian-made Soyuz rocket from the Guiana Space Center on the northern coast of South America. CHEOPS—pronounced KAY ops—is an acronym for Characterizing Exoplanets Satellite. If the acronym sounds familiar, Cheops was also the Greek name of the ancient Egyptian king Khufu, who constructed the Great Pyramid at Giza.

A Soyuz rocket carrying the ESA’s CHEOPS telescope lifts off from the Guiana Space Center on Dec.18, 2019. Credit: ESA/S. Corvaja

CHEOPS is small for a satellite, measuring just 5 feet (1.5 meters) long. The craft turns within a polar orbit that allows it to fly between night and day. Its back, covered in solar panels, receives continuous sunshine, while the telescope and camera on the other side is always peering into dark, sunless, and limitless space.

This artist’s impression shows CHEOPS with its back to the sun and the telescope pointed into dark space. Credit: ESA/C. Carreau

The CHEOPS mission is not to discover new exoplanets, but rather to learn more about the exoplanets we already know exist. CHEOPS will study exoplanets larger than our own Earth but smaller than the planet Neptune. Scientists want to know if these intermediate sized exoplanets are more like “super-Earths”—large rocky worlds—or “mini-Neptunes”—small gas giants. By studying an exoplanet’s atmosphere, diameter, mass, and other properties, CHEOPS can determine its composition and whether or not it might be able to support life. Astronomers have discovered over 4,000 exoplanets so far, but there are likely hundreds of billions more to be found.

CHEOPS will use the transit method to study exoplanets. It will aim its camera at a star and capture periodic dips in the star’s light output. These dips occur when an exoplanet passes in front of—or transits—a star in relation to CHEOPS’s point of view.

CHEOPS is a stepping stone between the first exoplanet observatories, such as Kepler and COROT, and the powerful observatories of the near future. The United States National Aeronautics and Space Administration (NASA) James Webb Space Telescope (JWST), scheduled for launch in 2021, will be able to determine the gases present in the atmospheres of some exoplanets and even record low detail images of those gases. The European Southern Observatory’s Extremely Large Telescope (ELT) will also be able to image rocky exoplanets and characterize their atmospheres after it is completed in 2025. The ELT is a ground-based observatory being built in the Atacama Desert of northern Chile. Kepler and COROT prepared the way for CHEOPS, and the JWST and ELT will further examine the most promising CHEOPS targets as scientists continue the hunt for extraterrestrial life.

October 11, 2019

Every year in the first week of October, the Nobel Foundation in Sweden awards Nobel Prizes to artists, economists, scientists, and peace workers who—in keeping with the vision of the Swedish chemist and industrialist Alfred Nobel—have conferred the greatest benefit to humankind. Today, World Book looks at the first three prizes, in the scientific categories of physiology or medicine, physics, and chemistry.

Nobel Prize medal (Credit: Nobel Foundation)

On Monday, October 7, 2019, the Nobel Prize in physiology or medicine was given jointly to the scientists William G. Kaelin, Jr., Sir Peter J. Ratcliffe, and Gregg L. Semenza for their work showing how cells adapt to the changing availability of oxygen. Kaelin, Ratcliffe, and Semenza identified the molecular machinery that allows cells to respond to changes in oxygen levels. Their discoveries offer promising new strategies in the treatment of such diseases and maladies as anemia, cancer, heart attacks, and strokes.

William G. Kaelin, Jr., was born in New York and is a professor of medicine at the Dana-Farber Cancer Institute in Boston and at the Brigham and Women’s Hospital at Harvard Medical School. Peter J. Ratcliffe of the United Kingdom is the director of clinical research at the Francis Crick Institute in London and director of the Target Discovery Institute at the University of Oxford. Gregg L. Semenza, also from New York, is a professor of genetic medicine at Johns Hopkins University in Baltimore, Maryland.

On Tuesday, October 8, the Nobel Foundation announced the prize for physics had been awarded to the Canadian-American cosmologist James Peebles and to the Swiss scientists Michel Mayor and Didier Queloz for their work on explaining the evolution of the universe and for discovering distant exoplanets (planets beyond our solar system). Among other things, Peebles theorized how matter in the young universe swirled into galaxies. In 1995, Mayor and Queloz discovered an exoplanet orbiting a star elsewhere in our home galaxy, the Milky Way, enhancing the study of planetary systems beyond our own that could support life.

James Peebles is the Albert Einstein professor of science at Princeton University in New Jersey. Michel Mayor is an astrophysicist and professor emeritus of astronomy at the University of Geneva. Didier Queloz is a professor of physics at the Cavendish Laboratory at Cambridge University, and at the University of Geneva.

On Wednesday, October 9, the Nobel Foundation announced that John B. Goodenough of the United States, M. Stanley Whittingham of the United Kingdom, and Akira Yoshino of Japan would share the prize for chemistry for developing and refining rechargeable lithium-ion batteries. The lightweight, rechargeable, and powerful batteries are used in everything from mobile phones to laptop computers and electric vehicles. They can also store great amounts of energy from solar and wind power, further enabling the possibility of a fossil fuel-free future.

At 97 years old, John B. Goodenough is the oldest ever recipient of the Nobel Prize. He is currently the Virginia H. Cockrell Chair in Engineering at the University of Texas at Austin. M. Stanley Whittingham is a distinguished professor at Binghamton University, State University of New York. Akira Yoshino is an honorary fellow at Tokyo’s Asahi Kasei Corporation and a professor at Meijo University in Nagoya, Japan.

September 13, 2019

Last week, on September 6, an up-and-coming space agency fell just short of its goal. About 1 mile (1.5 kilometers) above the moon’s surface, the India Space Research Organization (ISRO) lander Vikram deviated from its landing course and disappeared from radio contact. Vikram was to be the crowning stage of Chandrayaan-2 (Mooncraft-2), ISRO’s second lunar mission.

This artist’s depiction shows Chandrayaan-2′s lunar lander, Vikram, approaching the moon. Credit: © Raymond Cassel, Shutterstock

India was endeavoring to become the fourth country to make a soft landing (a landing that does not destroy the craft) on the surface of the moon, after the United States, the former Soviet Union, and China. Vikram would have been the first lander near the moon’s south pole, a region full of water ice and other minerals that could one day be the site of a permanent base. Vikram would have deployed a rover to explore the landing site. The Chandrayaan-2 orbiter, which had launched Vikram, located the lander on the surface of the moon a few days after its disappearance. ISRO reported that Vikram had apparently made a “hard landing,” and the lander did not respond to contact attempts.

Before the recent failure, ISRO had been riding a wave of success. In 2008, the agency deployed its first lunar satellite, Chandrayaan-1. Chandrayaan-1 mapped the moon’s surface for about a year. The satellite also released a hard lander that impacted the lunar surface. In 2013, ISRO launched the Mars Orbiter Mission, called Mangalyaan (Marscraft). The satellite overcame a minor engine failure to reach Martian orbit in September 2014.

ISRO’s failed soft landing on the moon comes on the heels of another prominent lunar failure. In April 2019, the lander Beresheet (In the Beginning), developed by the Israeli company SpaceIL, slammed into the moon when its main engine cut out unexpectedly. SpaceIL had hoped to become the first private company to place a lander on the moon’s surface. It had been one of the competitors for the Google Lunar X Prize. The contest would have awarded $20 million to the first company to achieve a soft landing on the moon. But none of the competitors attempted a landing, even after several deadline extensions, so the prize was withdrawn. The Israeli project cost about $100 million, a fraction of what a similar mission by the United States National Aeronautics and Space Administration (NASA) would have cost, but it took greater risks and ultimately failed.

The process of landing is the most dangerous phase of a lander’s mission. Many different systems must work perfectly for the lander to bring itself to a halt on the surface. Any malfunction is usually catastrophic. At other points in a mission, such as in transit to or in orbit around another body, engineers have plenty of time to identify and work around problems with a spacecraft. But this cannot be done in the time-sensitive environment of landing.

April 12, 2019

On Wednesday, April 10, scientists with the Event Horizon Telescope (EHT) team published a photograph of the invisible—or at least the area around the invisible. The EHT captured an image of an event horizon (the surface of a black hole) for the first time. The EHT is a global collection of radio telescopes that work together as one giant telescope. As its name implies, the EHT was created to observe an event horizon, a mission that has at last been accomplished. The EHT began its quest in 2006, and has since greatly expanded its network.

On April 10, 2019, scientists with the Event Horizon Telescope team released this first ever image of a black hole—or at least the event horizon surrounding a black hole. Credit: EHT Collaboration/ESO

A black hole is a region of space whose gravitational force is so strong that nothing can escape from it, not even light. The event horizon is the “point of no return” for a black hole: Anything that crosses this horizon is sucked into the black hole forever. Because light cannot escape a black hole, all black holes are invisible and cannot be directly photographed. But physicists predicted that an image of the area surrounding a black hole would reveal a halo of high-energy matter and radiation around a circular shadow.

The boxed area in this image shows the black hole at the core of the M87 galaxy.
Credit: NASA/CXC/Villanova University/J. Neilsen

Heino Falcke, a German astrophysicist now at Radboud University in the Netherlands, discovered that this halo would emit radio waves detectable on Earth. He helped found the EHT to photograph event horizons through these radio waves. The collection of ground-based radio telescopes participating in the EHT project stretches from Hawaii to Europe and all the way south to Antarctica. Several dozen of the world’s leading observatories and universities contribute to the project.

The EHT observed a supermassive black hole at the center of a huge galaxy called Messier 87, or M87, some 55 million lightyears from Earth. A supermassive black hole is a type of black hole with a mass from 1 million to billions of times the mass of our solar system’s  sun. Many galaxies have a supermassive black hole near their centers. The supermassive black hole at the center of M87 is one of the largest ever discovered, some 6.5 billion times the mass of our sun. The diameter of its event horizon is roughly the size of our entire solar system.

It took an enormous effort to produce the image released this April. Two years ago, in April 2017, eight radio telescopes of the EHT simultaneously observed the M87 black hole for 10 days. The observations had to be precisely synchronized (scheduled) by atomic clock to combine and match up their images. In total, the observatories collected more than 5 petabytes of data, equal to the text of 88 million print editions of the World Book Encyclopedia. (A petabyte is 1,000 terabytes. A terabyte is a measure of computer information or memory equal to about 1 trillion bytes). This was so much information that it was faster to fly the data by airplane between the laboratories that analyzed the data than to transfer it over the internet. An American computer scientist named Katie Bouman developed a special algorithm to combine the data from the eight telescopes into a single image.

Just like the detection of gravitational waves three years ago, this work promises to revolutionize astronomy. Each year, new observatories join the EHT, strengthening its resolution (image sharpness). The EHT has observed black holes other than the one at the core of M87, including the one at the center of our own Milky Way galaxy, Sagittarius A*. EHT scientists think they will be able to produce an image of that event horizon soon. Scientists might also be able to sharpen the image of the M87 black hole in the coming months.

August 9, 2018

Astronomers at the Carnegie Institution for Science in Washington, D.C., recently discovered a new batch of moons orbiting Jupiter, the largest planet in our solar system. The new group of 12 moons—which bring’s Jupiter’s moon total to an astounding 79—includes an oddball, however: one is going “the wrong way.”

Ganymede is the largest of Jupiter’s moons. Astronomers recently found 12 new and much smaller moons orbiting Jupiter, bringing the planet’s solar system-leading total to 79. Credit: NASA

Led by astronomer Scott Sheppard, the Carnegie team had been looking for “Planet Nine,” a hypothetical major planet in the Kuiper belt, a band of objects in the outer regions of our solar system. In March 2017, Jupiter moved into the astronomers’ search area. The telescope the team was using was uniquely suited for finding small or faraway objects: it could block out light from larger nearby heavenly bodies. Sheppard took time away from Planet Nine to poke around Jupiter, and his curiosity was rewarded with the discovery of 12 new moons. The first two bodies orbit close to Jupiter, and were quickly confirmed as moons. The other 10 skew farther out from the mighty planet and were not announced as moons until July 17, 2018.

Callisto, another large moon of Jupiter, has a diameter of almost 3,000 miles (4,800 kilometers), many times the size of Jupter’s newly discovered moons. Credit: NASA

The new moons are small, some less than a mile (several hundred meters) in diameter. Their orbital characteristics tell scientists a lot about them. Nine of the 10 newest moons orbit in retrograde, meaning in the opposite direction of the rotation of Jupiter. This leads the astronomers to think they formed from objects captured by Jupiter’s hefty gravitational pull. Most moons form with their parent planet and have prograde orbits, meaning they orbit in the same direction as the host planet. But captured objects often have retrograde orbits. Sheppard’s team thinks these nine moons are parts of captured objects broken up by collisions over millions or billions of years.

The tenth of the newest moons, however—which Sheppard calls Valetudo, a great-granddaughter of the Roman mythological god Jupiter—travels in a prograde orbit. It dives through the orbits of the other nine moons, putting it on an eventual collision course. When moon finally meets moon, the impact will either destroy the bodies or make them even smaller.

January 4, 2018

Astronomers at the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) observatory at the summit of the dormant volcano Haleakala in Hawaii recently detected a mysterious object speeding through our solar system. This by itself was not unusual. One of the main missions of the Pan-STARRS project is to detect near-Earth objects in space that could possibly collide with our planet. However, researchers quickly realized that this space rock did not move like the asteroids and comets they routinely encounter. Astronomers quickly learned that this object was a visitor from beyond our solar system—the first interstellar asteroid ever observed.

This artist’s impression shows `Oumuamua the interstellar asteroid. Credit: ESO/M. Kornmesser

Scientists at NASA’s Center for Near-Earth Object Studies (CNEOS) in Pasadena, California, determined the object was an asteroid, now officially designated as A/2017 UI. Its composition and its unusual path through our solar system showed it was from outer space. Researchers at Pan-STARRS named the asteroid `Oumuamua, which is a Hawaiian word that means messenger.

`Oumuamua appeared only as a faint spot on the Pan-STARRS telescope as it zipped through our solar system at up to 196,000 miles per hour (355,431 kilometers per hour). But later images from other observatories showed that `Oumuamua was 1,300 feet (400 meters) long and about 10 times as long as it was wide, and spinning rapidly. `Oumuamua’s elongated cigar shape is a rarity among space objects. Most asteroids are compact and lumpy after having been battered by countless random collisions with other objects on their long journeys through space. `Oumuamua is also dark red, a color created as its rocky surface was bombarded by high-energy cosmic rays for millions or perhaps billions of years. A/2017 UI traveled in a retrograde orbit (opposite that of the planets) around the sun on its way toward the constellation Pegasus.

Some researchers suggested that `Oumuamua was more than just an interstellar oddity, and that it was perhaps a message from a distant alien civilization. They pointed out that “a cigar or needle shape is the most likely architecture for an interstellar spacecraft, since this would minimize friction and damage from interstellar gas and dust.” Several groups scanned `Oumuamua for alien radio transmissions, including researchers at the Green Bank Telescope in West Virginia, the William Herschel Telescope in Spain’s Canary Islands, and the European Southern Observatory’s Very Large Telescope in Chile. No alien messages were found, and the consensus was that `Oumuamua was odd but completely natural. Scientists suspect that the so-called “space cucumber” has an icy core—as do most comets—beneath its hard carbonic shell.

October 27, 2017

On August 17, a faint chirp from instruments at the Laser Interferometer Gravitational-wave Observatory (LIGO) in the United States set off a mad scramble in observatories around the world to catch a glimpse of something never before observed: the cosmic collision of two neutron stars (an event called a kilonova). In the extraordinary events that followed, the signal initially detected by LIGO was picked up by as many as 70 Earth and space-based telescopes, providing a remarkably detailed picture of one of the most violent, cataclysmic events in the universe. The significant observation was announced by LIGO scientists on October 16.

This artist’s representation shows two neutron stars colliding, a cataclysmic event known as a kilonova. Astronomers witnessed a kilonova for the first time on Aug. 17, 2017. Credit: © Robin Dienel, Carnegie Institution for Science

LIGO is a pair of facilities built to detect gravitational waves, types of radiation created by the movement of matter through space. LIGO consists of three detectors—two near Richland, Washington, and one in Livingston, Louisiana. The LIGO detectors are designed to find gravitational waves created by such violent cosmic events as collisions between black holes, objects with gravitational forces so strong that nothing can escape them. The first gravitational waves were detected by LIGO on Sept. 14, 2015. The waves were generated by colliding black holes billions of light-years away from Earth.

The recent kilonova observation was significant for several reasons. It was the first time LIGO had detected the weaker gravitational wave generated by a collision between neutron stars, the smallest and densest types of known stars. The kilonova signal was also detected at the European Gravitational Observatory (EGO) interferometer, called Virgo, located near Pisa, Italy. With data from multiple observatories, astronomers were able to determine the starting point of the gravitational wave. As word of the signal spread, dozens of other telescopes on Earth and in space were trained on the location to detect other kinds of energy from the cosmic collision. Astronomers were able to observe the resulting fireball in visible light from telescopes. Other telescopes recorded the gamma rays, radio waves, ultraviolet rays, and X rays generated from the collision. It was the first time such a cosmic event had been seen by astronomers, witnessed in wavelengths across the electromagnetic spectrum.

The gravitational wave signal detected by LIGO came from two neutron stars orbiting each other about 130 million light-years away. Each neutron star had slightly more mass than our own sun, but all that mass was crammed into a sphere only about 20 miles (32 kilometers) in diameter. The doomed stars circled each other 30 times a second as they neared to within about 200 miles (320 kilometers) of each other. The orbit increased to about 2,000 times per second just before they collided in an impact that released a tremendous burst of energy. What happened next is uncertain. Scientists think that after the stars collided they may have formed a heavier neutron star or collapsed into a black hole.

Some telescopes were able to spot a faint flash in the night sky. That flash was generated in the fireball of the collision as radioactive heavy chemical elements were blown away at nearly one-fifth the speed of light. Scientists had long theorized that such catastrophic celestial collisions were necessary to forge heavy chemical elements, such as gold, platinum, and uranium. The spectrum of light coming from the observed collision of neutron stars helped confirm this theory. They calculated that the explosion created about 100 times the mass of Earth in gold. Scientists now believe such collisions of neutron stars are common in the universe. They believe that most heavy element atoms in the universe are formed in such kilonova events.