The heliosphere is the bubble-like region of space dominated by the Sun, which extends far beyond the orbit of Pluto. Plasma “blown” out from the Sun, known as the solar wind, creates and maintains this bubble against the outside pressure of the interstellar medium, the hydrogen and helium gas that permeates the Milky Way Galaxy. The solar wind flows outward from the Sun until encountering the termination shock, where motion slows abruptly. The Voyager spacecraft have explored the outer reaches of the heliosphere, passing through the shock and entering the heliosheath, a transitional region which is in turn bounded by the outermost edge of the heliosphere, called the heliopause.
The shape of the heliosphere is controlled by the interstellar medium
through which it is traveling, as well as the Sun and is not perfectly
spherical. The limited data available and unexplored nature of these structures have resulted in many theories. The word “heliosphere” is said to have been coined by Alexander J. Dessler, who is credited with first use of the word in the scientific literature.
On September 12, 2013, NASA announced that Voyager 1 left the heliopause on August 25, 2012, when it measured a sudden increase in plasma density of about forty times. Because the heliopause marks one boundary
between the Sun’s solar wind and the rest of the galaxy, a spacecraft
such as Voyager 1 which has departed the heliosphere, can be said to
have reached interstellar space. source
Saturn and its moons at opposition (The visible moons are (from left to right) Dione, Enceladus, Tethys, Janus, Epimetheus and Mimas
NASA, ESA, A. Simon (GSFC) and the OPAL Team, and J. DePasquale (STScI)
On this day in 1977 was launched the space probe Voyager 1.
Voyager 1 is a space probe launched by NASA on September 5, 1977. Part of the Voyager program to study the outer Solar System, Voyager 1 launched 16 days after its twin, Voyager 2. Having operated for 41 years as of September 5, 2018, the spacecraft still communicates with the Deep Space Network to receive routine commands and return data. At a distance of 142.31 astronomical units from the Sun as of June 4, 2018, it is the most distant man-made object from Earth.
The probe’s objectives included flybys of Jupiter, Saturn, and Saturn’s largest moon, Titan. While the spacecraft’s course could have been altered to include a Pluto encounter by forgoing the Titan flyby, exploration of the moon, which was known to have a substantial atmosphere, took priority. It studied the weather, magnetic fields and rings of the two planets and was the first probe to provide detailed images of their moons. (read more)
Voyager 1 Trajectory through the Solar System
Saturn’s moon Enceladus, covered in snow and ice, resembles a perfectly packed snowball in this image from NASA’s Cassini mission.
Image credit: NASA/JPL-Caltech/Space Science Institute
Neptune (red arc) completes one orbit around the Sun (center) for every 164.79 orbits of Earth. The light blue object represents Uranus.
On August 8, 1978, the Pioneer Venus Multiprobe spacecraft launched to study Venus, a planet that has an atmosphere 100 times denser than Earth’s atmosphere and is hotter than the melting point of zinc and lead. Pioneer Venus Multiprobe was composed of five components: the main spacecraft, the large probe and three identical small probes named North, Day and Night. Built by the Hughes Company in El Segundo, California, and launched on an Atlas-Centaur rocket from Cape Canaveral Air Force Station in Florida, the Pioneer Venus Multiprobe project was managed by NASA’s Ames Research Center in California’s Silicon Valley.
Carrying seven experiments and fitted with a parachute to slow its descent into the atmosphere, the large probe studied the composition of Venus’ atmosphere and clouds. In addition, the large probe measured the distribution of infrared and solar radiation. The three small probes were designed without parachutes, each carrying six experiments. Each probe targeted different parts of Venus. North entered Venus at the high northern latitudes, Night targeted the night side at mid-southern latitudes, and Day targeted the day side at mid-southern latitudes. The main spacecraft carried an additional two experiments designed to study Venus’ upper atmosphere. The five probes collected detailed information about atmospheric composition, circulation and energy balance.
The large probe separated from the main spacecraft 123 days after launch, on November 16, followed by the small probes on November 20, reaching and entering Venus’ atmosphere December 9. While not expected to survive their fiery descent into the dense Venusian atmosphere, all four of the probes transmitted data down to the surface with the Day probe transmitting from the surface for over an hour.
This image shows the recent observations of the planets Mars and Saturn made with the NASA/ESA Hubble Space Telescope. The observations of both objects were made in June and July 2018 and show the planets close to their opposition.
Credit: NASA/ESA, Hubble
Jupiter and Io taken by the Cassini spacecraft on December 1, 2000.
Credit: NASA/JPL/University of Arizona
This image of the planet Neptune was obtained during the testing of the Narrow-Field adaptive optics mode of the MUSE/GALACSI instrument on ESO’s Very Large Telescope. The corrected image is sharper than a comparable image from the NASA/ESA Hubble Space Telescope.
Credit: ESO/P. Weilbacher (AIP)