The rings of Saturn may be iconic, but there was a time when the majestic gas giant existed without its distinctive halo. In fact, the rings may have formed much later than the planet itself, according to a new analysis of gravity science data from NASA’s Cassini spacecraft.
The findings indicate that Saturn’s rings formed between 10 million and 100 million years ago. From our planet’s perspective, that means Saturn’s rings may have formed during the age of dinosaurs.
The conclusions of the research – gleaned from measurements collected during the final, ultra-close orbits Cassini performed in 2017 as the spacecraft neared the end of its mission – are the best answer yet to a longstanding question in solar system science. The findings were published online Jan. 17 in Science.
DC Agle Jet Propulsion Laboratory, Pasadena, Calif.
Dwayne Brown / Laurie Cantillo NASA Headquarters, Washington
NASA’s Juno spacecraft will make its fifth flyby over Jupiter’s mysterious cloud tops on Monday, March 27, at 1:52 a.m. PDT (4:52 a.m. EDT, 8:52 UTC).
At the time of closest approach (called perijove), Juno will be about 2,700 miles (4,400 kilometers) above the planet’s cloud tops, traveling at a speed of about 129,000 miles per hour (57.8 kilometers per second) relative to the gas-giant planet. All of Juno’s eight science instruments will be on and collecting data during the flyby.
Imagine you want to measure the size of a room, but it’s completely dark. If you shout, you can tell if the space you’re in is relatively big or small, depending on how long it takes to hear the echo after it bounces off the wall.
Astronomers use this principle to study objects so distant they can’t be seen as more than points. In particular, researchers are interested in calculating how far young stars are from the inner edge of their surrounding protoplanetary disks. These disks of gas and dust are sites where planets form over the course of millions of years.
This Saturday at 5:51 a.m. PDT, (8:51 a.m. EDT, 12:51 UTC) NASA’s Juno spacecraft will get closer to the cloud tops of Jupiter than at any other time during its prime mission. At the moment of closest approach, Juno will be about 2,600 miles (4,200 kilometers) above Jupiter’s swirling clouds and traveling at 130,000 mph (208,000 kilometers per hour) with respect to the planet. There are 35 more close flybys of Jupiter scheduled during its prime mission (scheduled to end in February of 2018). The Aug. 27 flyby will be the first time Juno will have its entire suite of science instruments activated and looking at the giant planet as the spacecraft zooms past.
“This is the first time we will be close to Jupiter since we entered orbit on July 4,” said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. “Back then we turned all our instruments off to focus on the rocket burn to get Juno into orbit around Jupiter. Since then, we have checked Juno from stem to stern and back again. We still have more testing to do, but we are confident that everything is working great, so for this upcoming flyby Juno’s eyes and ears, our science instruments, will all be open.”
“This is our first opportunity to really take a close-up look at the king of our solar system and begin to figure out how he works,” Bolton said.
While the science data from the pass should be downlinked to Earth within days, interpretation and first results are not expected for some time.
“No other spacecraft has ever orbited Jupiter this closely, or over the poles in this fashion,” said Steve Levin, Juno project scientist from NASA’s Jet Propulsion Laboratory in Pasadena, California. “This is our first opportunity and there are bound to be surprises. We need to take our time to make sure our conclusions are correct.”
Not only will Juno’s suite of eight science instruments be on, the spacecraft’s visible light imager — JunoCam will also be snapping some closeups. A handful of JunoCam images, including the highest resolution imagery of the Jovian atmosphere and the first glimpse of Jupiter’s north and south poles, are expected to be released during the later part of next week.
The Juno spacecraft launched on Aug. 5, 2011, from Cape Canaveral, Florida. JPL manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for NASA’s Science Mission Directorate. Lockheed Martin Space Systems, Denver, built the spacecraft. Caltech, in Pasadena, California, manages JPL for NASA.
Note from George McGinn: Yesterday I watched NASA’s briefing, and the Juno Spacecraft did something nearly impossible. The largest danger to the mission is the immense radiation. Jupiter’s version of Earth’s Van Allen belt have been catching huge amounts of solar radiation for 4.5 billion years. The gravity of Jupiter is so strong that it pulls more charged particles than would directly hit it. The Juno team estimated that the spacecraft will be exposed to radiation at LD25 (LD is Leathal Dose and 25 means 25 times, so 25 times the lethal dose to a human), or having 1 million dental X-rays all at once (in a space of 2 seconds). This is equal to 260 rads.
I applaud the Juno’s team, who worked almost 12 years to get this spacecraft safely in orbit. I am excited to see finally how deep the atmosphere goes, what gases make up Jupiter, and if there is a solid or semi-solid center, or just compressed gases. And can all that gas create the large magnetic field, or what is in the center, the speed of spin, and the chemical makeup.
After an almost five-year journey to the solar system’s largest planet, NASA’s Juno spacecraft successfully entered Jupiter’s orbit during a 35-minute engine burn. Confirmation that the burn had completed was received on Earth at 8:53 pm. PDT (11:53 p.m. EDT) Monday, July 4.
“Independence Day always is something to celebrate, but today we can add to America’s birthday another reason to cheer — Juno is at Jupiter,” said NASA Administrator Charlie Bolden. “And what is more American than a NASA mission going boldly where no spacecraft has gone before? With Juno, we will investigate the unknowns of Jupiter’s massive radiation belts to delve deep into not only the planet’s interior, but into how Jupiter was born and how our entire solar system evolved.”
Confirmation of a successful orbit insertion was received from Juno tracking data monitored at the navigation facility at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, as well as at the Lockheed Martin Juno operations center in Denver. The telemetry and tracking data were received by NASA’s Deep Space Network antennas in Goldstone, California, and Canberra, Australia.
“This is the one time I don’t mind being stuck in a windowless room on the night of the Fourth of July,” said Scott Bolton, principal investigator of Juno from Southwest Research Institute in San Antonio. “The mission team did great. The spacecraft did great. We are looking great. It’s a great day.”
Preplanned events leading up to the orbital insertion engine burn included changing the spacecraft’s attitude to point the main engine in the desired direction and then increasing the spacecraft’s rotation rate from 2 to 5 revolutions per minute (RPM) to help stabilize it..
The burn of Juno’s 645-Newton Leros-1b main engine began on time at 8:18 p.m. PDT (11:18 p.m. EDT), decreasing the spacecraft’s velocity by 1,212 mph (542 meters per second) and allowing Juno to be captured in orbit around Jupiter. Soon after the burn was completed, Juno turned so that the sun’s rays could once again reach the 18,698 individual solar cells that give Juno its energy.
“The spacecraft worked perfectly, which is always nice when you’re driving a vehicle with 1.7 billion miles on the odometer,” said Rick Nybakken, Juno project manager from JPL. “Jupiter orbit insertion was a big step and the most challenging remaining in our mission plan, but there are others that have to occur before we can give the science team members the mission they are looking for.”
Over the next few months, Juno’s mission and science teams will perform final testing on the spacecraft’s subsystems, final calibration of science instruments and some science collection.
“Our official science collection phase begins in October, but we’ve figured out a way to collect data a lot earlier than that,” said Bolton. “Which when you’re talking about the single biggest planetary body in the solar system is a really good thing. There is a lot to see and do here.”
Juno’s principal goal is to understand the origin and evolution of Jupiter. With its suite of nine science instruments, Juno will investigate the existence of a solid planetary core, map Jupiter’s intense magnetic field, measure the amount of water and ammonia in the deep atmosphere, and observe the planet’s auroras. The mission also will let us take a giant step forward in our understanding of how giant planets form and the role these titans played in putting together the rest of the solar system. As our primary example of a giant planet, Jupiter also can provide critical knowledge for understanding the planetary systems being discovered around other stars.
The Juno spacecraft launched on Aug. 5, 2011, from Cape Canaveral Air Force Station in Florida. JPL manages the Juno mission for NASA. Juno is part of NASA’s New Frontiers Program, managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate. Lockheed Martin Space Systems in Denver built the spacecraft. The California Institute of Technology in Pasadena manages JPL for NASA.
In 1936, the young star FU Orionis began gobbling material from its surrounding disk of gas and dust with a sudden voraciousness. During a three-month binge, as matter turned into energy, the star became 100 times brighter, heating the disk around it to temperatures of up to 12,000 degrees Fahrenheit (7,000 Kelvin). FU Orionis is still devouring gas to this day, although not as quickly.
This brightening is the most extreme event of its kind that has been confirmed around a star the size of the sun, and may have implications for how stars and planets form. The intense baking of the star’s surrounding disk likely changed its chemistry, permanently altering material that could one day turn into planets.
“By studying FU Orionis, we’re seeing the absolute baby years of a solar system,” said Joel Green, a project scientist at the Space Telescope Science Institute, Baltimore, Maryland. “Our own sun may have gone through a similar brightening, which would have been a crucial step in the formation of Earth and other planets in our solar system.”
Visible light observations of FU Orionis, which is about 1,500 light-years away from Earth in the constellation Orion, have shown astronomers that the star’s extreme brightness began slowly fading after its initial 1936 burst. But Green and colleagues wanted to know more about the relationship between the star and surrounding disk. Is the star still gorging on it? Is its composition changing? When will the star’s brightness return to pre-outburst levels?
To answer these questions, scientists needed to observe the star’s brightness at infrared wavelengths, which are longer than the human eye can see and provide temperature measurements.
Green and his team compared infrared data obtained in 2016 using the Stratospheric Observatory for Infrared Astronomy, SOFIA, to observations made with NASA’s Spitzer Space Telescope in 2004. SOFIA, the world’s largest airborne observatory, is jointly operated by NASA and the German Aerospace Center and provides observations at wavelengths no longer attainable by Spitzer. The SOFIA data were taken using the FORCAST instrument (Faint Object infrared Camera for the SOFIA Telescope).
“By combining data from the two telescopes collected over a 12-year interval, we were able to gain a unique perspective on the star’s behavior over time,” Green said. He presented the results at the American Astronomical Society meeting in San Diego, this week.
Using these infrared observations and other historical data, researchers found that FU Orionis had continued its ravenous snacking after the initial brightening event: The star has eaten the equivalent of 18 Jupiters in the last 80 years.
The recent measurements provided by SOFIA inform researchers that the total amount of visible and infrared light energy coming out of the FU Orionis system decreased by about 13 percent over the 12 years since the Spitzer observations. Researchers determined that this decrease is caused by dimming of the star at short infrared wavelengths, but not at longer wavelengths. That means up to 13 percent of the hottest material of the disk has disappeared, while colder material has stayed intact.
“A decrease in the hottest gas means that the star is eating the innermost part of the disk, but the rest of the disk has essentially not changed in the last 12 years,” Green said. “This result is consistent with computer models, but for the first time we are able to confirm the theory with observations.”
Astronomers predict, partly based on the new results, that FU Orionis will run out of hot material to nosh on within the next few hundred years. At that point, the star will return to the state it was in before the dramatic 1936 brightening event. Scientists are unsure what the star was like before or what set off the feeding frenzy.
“The material falling into the star is like water from a hose that’s slowly being pinched off,” Green said. “Eventually the water will stop.”
If our sun had a brightening event like FU Orionis did in 1936, this could explain why certain elements are more abundant on Mars than on Earth. A sudden 100-fold brightening would have altered the chemical composition of material close to the star, but not as much farther from it. Because Mars formed farther from the sun, its component material would not have been heated up as much as Earth’s was.
At a few hundred thousand years old, FU Orionis is a toddler in the typical lifespan of a star. The 80 years of brightening and fading since 1936 represent only a tiny fraction of the star’s life so far, but these changes happened to occur at a time when astronomers could observe.
“It’s amazing that an entire protoplanetary disk can change on such a short timescale, within a human lifetime,” said Luisa Rebull, study co-author and research scientist at the Infrared Processing and Analysis Center (IPAC), based at Caltech, Pasadena, California.
Green plans to gain more insight into the FU Orionis feeding phenomenon with NASA’s James Webb Space Telescope, which will launch in 2018. SOFIA has mid-infrared high-resolution spectrometers and far-infrared science instrumentation that complement Webb’s planned near- and mid-infrared capabilities. Spitzer is expected to continue exploring the universe in infrared light, and enabling groundbreaking scientific investigations, into early 2019.
NASA’s Jet Propulsion Laboratory, Pasadena, California, manages the Spitzer Space Telescope mission for NASA. Science operations are conducted at the Spitzer Science Center at Caltech. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.
SOFIA is a joint project of NASA and the German Aerospace Center (DLR). The aircraft is based at NASA Armstrong Flight Research Center’s facility in Palmdale, California. NASA’s Ames Research Center in Moffett Field, California, manages the SOFIA science and mission operations in cooperation with the Universities Space Research Association (USRA) headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart.