This illustration shows the events that occur in the final minutes of the nearly seven-month journey that NASA’s Perseverance rover takes to Mars. Hundreds of critical events must execute perfectly and exactly on time for the rover to land on Mars safely on Feb. 18, 2021.
Entry, Descent, and Landing, or “EDL,” begins when the spacecraft reaches the top of the Martian atmosphere, traveling nearly 12,500 mph (20,000 kph). It ends about seven minutes later, with Perseverance stationary on the Martian surface. Perseverance handles everything on its own during this process. It takes more than 11 minutes to get a radio signal back from Mars, so by the time the mission team hears that the spacecraft has entered the atmosphere, in reality, the rover is already on the ground.
NASA’s Jet Propulsion Laboratory in Southern California built and will manage operations of the Mars 2020 Perseverance rover for NASA.
“Looping through the Jovian system in the late 1990s, the Galileo spacecraft recorded stunning views of Europa and uncovered evidence that the moon’s icy surface likely hides a deep, global ocean. Galileo‘s Europa image data has been remastered here, using improved new calibrations to produce a color image approximating what the human eye might see. Europa’s long curving fractures hint at the subsurface liquid water. The tidal flexing the large moon experiences in its elliptical orbit around Jupiter supplies the energy to keep the ocean liquid. But more tantalizing is the possibility that even in the absence of sunlight that process could also supply the energy to support life, making Europa one of the best places to look for life beyond Earth. What kind of life could thrive in a deep, dark, subsurface ocean?” — Via APOD: Astronomy Picture Of the Day
For the second time in history, a human-made object has reached the space between the stars. NASA’s Voyager 2 probe now has exited the heliosphere – the protective bubble of particles and magnetic fields created by the Sun.
Comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on Nov. 5. This boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Its twin, Voyager 1, crossed this boundary in 2012, but Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.
Voyager 2 now is slightly more than 11 billion miles (18 billion kilometers) from Earth. Mission operators still can communicate with Voyager 2 as it enters this new phase of its journey, but information – moving at the speed of light – takes about 16.5 hours to travel from the spacecraft to Earth. By comparison, light traveling from the Sun takes about eight minutes to reach Earth.
The most compelling evidence of Voyager 2’s exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980, long before that probe crossed the heliopause. Until recently, the space surrounding Voyager 2 was filled predominantly with plasma flowing out from our Sun. This outflow, called the solar wind, creates a bubble – the heliosphere – that envelopes the planets in our solar system. The PLS uses the electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on Nov. 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which makes mission scientists confident the probe has left the heliosphere.
“Working on Voyager makes me feel like an explorer, because everything we’re seeing is new,” said John Richardson, principal investigator for the PLS instrument and a principal research scientist at the Massachusetts Institute of Technology in Cambridge. “Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time, and without the PLS data. So we’re still seeing things that no one has seen before.”
In addition to the plasma data, Voyager’s science team members have seen evidence from three other onboard instruments – the cosmic ray subsystem, the low energy charged particle instrument and the magnetometer – that is consistent with the conclusion that Voyager 2 has crossed the heliopause. Voyager’s team members are eager to continue to study the data from these other onboard instruments to get a clearer picture of the environment through which Voyager 2 is traveling.
“There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” said Ed Stone, Voyager project scientist based at Caltech in Pasadena, California.
“Voyager has a very special place for us in our heliophysics fleet,” said Nicola Fox, director of the Heliophysics Division at NASA Headquarters. “Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun’s influence gives us an unprecedented glimpse of truly uncharted territory.”
While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won’t be leaving anytime soon. The boundary of the solar system is considered to be beyond the outer edge of the Oort Cloud, a collection of small objects that are still under the influence of the Sun’s gravity. The width of the Oort Cloud is not known precisely, but it is estimated to begin at about 1,000 astronomical units (AU) from the Sun and to extend to about 100,000 AU. One AU is the distance from the Sun to Earth. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort Cloud and possibly 30,000 years to fly beyond it.