domingo, 23 de agosto de 2015

NASA WEB ·QUASAR HOST GALAXIES-This process would explain the occurrence of quasars with redshift. In the far distant past there were no galaxies, so no sites for quasars. In the early phases of galaxy formation, the galaxy density was high, and there were many collisions producing many quasars. As time passed, the number of collisions decreased as space expanded and the number of quasar also dropped.

Seyfert Galaxies:Readings: Seyfert Galaxies
Radio Galaxies
In 1943, Carl Seyfert published a list of 12 otherwise normal spiral galaxies which contain anomalously bright central nuclei. These galaxies are now known as "Seyferts", a subclass of what is now called active galaxies. The following figure shows successively deeper images of the Seyfert galaxy NGC4151. In short exposures, only the bright nucleus is apparent, but deeper images reveal the normal spiral galaxy around it. In some Seyferts, the central nucleus outshines the whole surrounding galaxy.
The central nucleus light output varies on timescales of less than a year So, the emitting region must be less than a light year across, as the source cannot vary coherently on timescales shorter than this due to light travel time effects.
This central region of excess radiation is attributed to the active galactic nucleus (AGN). The engine that powers the AGN must produce tremendous amounts of energy and the best candidate appears to be an accreting supermassive blackhole. The gravitational energy of infalling matter is converted into electromagnetic radiation and emitted at all wavelengths. This separates active galaxies from normal galaxies. Normal galaxies emit most of their energy as a thermal blackbody curve due to stars and glowing gas. Active galaxies also emit an extra component due to the blackhole, both in the radio region of the spectrum by synchrotron radiation (non-thermal) and hard x-ray from the hot accretion disk.
Spectra of the nuclei in Seyferts are non-stellar in nature and display information concerning the emitting regions. From the Doppler effect, spectral lines that are broad in wavelength are emitted from gas clouds moving with high velocities. Likewise, low velocity clouds emit narrow lines. The spectra of Seyfert galaxies typically contain:
  • Non-thermal continuum emission
  • Narrow (=> low velocity), forbidden (=> low density material) lines which do not vary detectably (=> large emitting region)
  • Broad (=> high velocity), permitted lines which vary on fairly short timescales (=> small emitting region)
  • Also, strong emission in the radio, infrared, ultraviolet, and X-ray parts of the spectrum.
Forbidden lines are spectral lines which are very improbable (not really forbidden). Their emission indicates very low densities in order for the electrons to survive in higher orbits without collisions long enough to emit rare wavelengths.
Seyfert galaxies have been classified into two basic types:
  • Seyfert 1 galaxies are bright in the optical, and have both broad and narrow lines in their spectra.
  • Seyfert 2 galaxies are fainter in the optical (but the same as Seyfert 1s in the infrared), and they only have narrow lines in their spectra.
In the broad-line region (BLR):
  • The Keplerian orbital speeds of the clouds around the central massive body will be large => lines are Doppler broadened.
  • Density is high => no forbidden lines are emitted
In the narrow-line region (NLR)
  • The Keplerian orbital speeds of the clouds will be much smaller => lines are narrow
  • Density is low => forbidden lines are emitted
  • So, if the above Seyfert were viewed from direction (1), you would see:
    • Broad permitted lines
    • Narrow Forbidden Lines
    • Bright continuum from the central engine
    • i.e. a Seyfert 1
  • If, on the other hand, it were viewed from direction (2), you would see:
    • No broad permitted lines (obscured by dust torus)
    • Narrow Forbidden Lines
    • No bright continuum from the obscured central engine
      • except in the infrared and X-ray region, which gets through the dust
    • i.e. a Seyfert 2

Radio Galaxies:
As radio astronomers mapped the sky, they found several bright radio sources associated with distant galaxies. One of the brightest was the radio source Cygnus A. Cygnus A is a double-lobed radio source. Also notice the jets from the center. At the center sits a giant elliptical galaxy, at a distance of ~ 200 Mpc. At this distance, the lobes are separated by more than 100 kpc, and they have a radio luminosity of 1045 erg/s, 106 times greater than the radio luminosity of normal galaxies. Radio galaxies, unlike Seyferts, are generally hosted by elliptical galaxies, not spirals. Seyferts are also radio quiet.
M87, the central elliptical in Virgo, also is a radio galaxy. It is close enough that we can examine its center in detail, where we can actually see the jet in the optical.
These observations and arguments all suggest that active galaxies are powered by material accreting onto a massive central black hole in the nuclei of galaxies:
  • Accretion disk: hot, luminous gas falling into the black hole
  • Jets: charged particles moving at relativistic speeds out of the nucleus
  • Broad-line clouds: Gas clouds near the accretion disk, turbulent motions at high speed
  • Dusty torus: a ring of denser gas and dust surrounding the nucleus.
  • Narrow-line clouds: Gas clouds further out, moving more slowly
To achieve the necessary luminosity, ~ 1-10 Msun/yr must be accreted onto the black hole. Under this model, Seyfert galaxies, radio galaxies, and quasars are similar objects -- accretion powered active nuclei. They may differ in total luminosity (quasars vs seyferts) or in radio power (seyferts vs quasars/radio galaxies) or in host galaxies (seyferts vs radio galaxies).

Quasi-Stellar Objects, QSOs, or Quasars are the most luminous objects in the Universe. The typical quasar emits 100 to 1000 times the amount of radiation as our own Milky Way galaxy. However, quasars are also variable on the order of a few days, which means that the source of radiation must be contained in a volume of space on a few light-days across. How such amounts of energy can be generated in such small volumes is a challenge to our current physics.
Quasars were originally discovered in the radio region of the spectrum, even though they emit most of their radiation in the high energy x-ray and gamma-ray regions. Optical spectra of the first quasars in the 1960's showed them to be over two billion light-years away, meaning two billion years into the past as well.
Over a thousand quasars have been discovered, most having redshifts greater than 10 billion light-years away. The number density of quasars drops off very fast, such that they are objects associated with a time when galaxies were young.
HST imaging showed that quasars are centered in the middle of host galaxies, giving more support to the idea that the quasar phenomenon is associated with Galactic mass black holes in the middle of the host galaxies. Since a majority of the host galaxies are disturbed in appearance, the suspicion is that colliding galaxies cause stars and gas to be tidally pushed into the black hole to fuel the quasar.
This process would explain the occurrence of quasars with redshift. In the far distant past there were no galaxies, so no sites for quasars. In the early phases of galaxy formation, the galaxy density was high, and there were many collisions producing many quasars. As time passed, the number of collisions decreased as space expanded and the number of quasar also dropped.

sábado, 22 de agosto de 2015

NASA WEB ·NASA's Kepler Mission Discovers Bigger, Older Cousin to Earth

This size and scale of the Kepler-452 system compared alongside the Kepler-186 system and the solar system
Artist's concept depicts one possible appearance of the planet Kepler-452b

The artist's concept compares Earth (left) to the new planet, called Kepler-452b
This artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. Image credit: NASA Ames/JPL-Caltech 
› Full image and caption | › See animated gif
NASA's Kepler mission has confirmed the first near-Earth-size planet in the "habitable zone" around a sun-like star. This discovery and the introduction of 11 other new small habitable-zone candidate planets mark another milestone in the journey to finding another "Earth."
The newly discovered Kepler-452b is the smallest planet to date discovered orbiting in the habitable zone -- the area around a star where liquid water could pool on the surface of an orbiting planet -- of a G2-type star, like our sun. The confirmation of Kepler-452b brings the total number of confirmed planets to 1,030.
"On the 20th anniversary year of the discovery that proved other suns host planets, the Kepler exoplanet explorer has discovered a planet and star which most closely resemble the Earth and our sun," said John Grunsfeld, associate administrator of NASA's Science Mission Directorate at the agency's headquarters in Washington. "This exciting result brings us one step closer to finding an Earth 2.0."
Kepler-452b has a diameter 60 percent larger than Earth and is considered a super-Earth-size planet. While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a good chance of being rocky.
While Kepler-452b is larger than Earth, its 385-day orbit is only 5 percent longer. The planet is 5 percent farther from its parent star, Kepler-452, than Earth is from the sun. Kepler-452 is 6 billion years old, 1.5 billion years older than our sun, has the same temperature, and is 20 percent brighter, with a diameter 10 percent larger.
"We can think of Kepler-452b as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth's evolving environment," said Jon Jenkins, Kepler data analysis lead at NASA's Ames Research Center in Moffett Field, California, who led the team that discovered Kepler-452b. "It's awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star; longer than Earth. That's substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet."
To help confirm the finding and better determine the properties of the Kepler-452 system, the team conducted ground-based observations at the University of Texas at Austin's McDonald Observatory, the Fred Lawrence Whipple Observatory on Mt. Hopkins, Arizona, and the W. M. Keck Observatory atop Mauna Kea in Hawaii. These measurements were key for the researchers to confirm the planetary nature of Kepler-452b, to refine the size and brightness of its host star and to better pin down the size of the planet and its orbit.
The Kepler-452 system is located 1,400 light-years away in the constellation Cygnus. The research paper reporting this finding has been accepted for publication in The Astronomical Journal.
In addition to confirming Kepler-452b, the Kepler team has increased the number of new exoplanet candidates by 521 from their analysis of observations conducted from May 2009 to May 2013, raising the number of planet candidates detected by the Kepler mission to 4,696. Candidates require follow-up observations and analysis to verify they are actual planets.
Twelve of the new planet candidates have diameters between one to two times that of Earth, and orbit in their star's habitable zone. Of these, nine orbit stars that are similar to our sun in size and temperature.
"We've been able to fully automate our process of identifying planet candidates, which means we can finally assess every transit signal in the entire Kepler dataset quickly and uniformly," said Jeff Coughlin, Kepler scientist at the SETI Institute in Mountain View, California, who led the analysis of a new candidate catalog. "This gives astronomers a statistically sound population of planet candidates to accurately determine the number of small, possibly rocky planets like Earth in our Milky Way galaxy."
These findings, presented in the seventh Kepler Candidate Catalog, will be submitted for publication in the Astrophysical Journal. These findings are derived from data publicly available on the NASA Exoplanet Archive.
Scientists now are producing the last catalog based on the original Kepler mission's four-year data set. The final analysis will be conducted using sophisticated software that is increasingly sensitive to the tiny telltale signatures of Earth-size planets.
Ames manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

NASA WEB ·Colorful Calendar Celebrates 12th Anniversary of NASA's Spitzer

Spitzer Turns 12

Seeing Beyond the 'Monkey Head'
NASA's Spitzer Space Telescope is celebrating 12 years in space with a new digital calendar. The calendar's 12 images are shown here. Image credit: NASA/JPL-Caltech
› Larger image
Celebrate the 12th anniversary of NASA's Spitzer Space Telescope with a new digital calendar showcasing some of the mission's most notable discoveries and popular cosmic eye candy.
The calendar follows the life of the mission, with each month highlighting top infrared images and discoveries from successive years -- everything from a dying star resembling the eye of a monster to a star-studded, swirling galaxy. The final month includes a brand new image of the glittery star-making factory known as the Monkey Head nebula.
"You can't fully represent Spitzer's scientific bounty in only 12 images," said Michael Werner of NASA's Jet Propulsion Laboratory in Pasadena, California, the mission's project scientist and a Spitzer team member since 1977. "But these gems demonstrate Spitzer's unique perspectives on both the nearest, and the most distant, objects in the universe."
Spitzer, which launched into space on August 25, 2003, from Cape Canaveral, Florida, is still going strong. It continues to use its ultra-sensitive infrared vision to probe asteroids, comets, exoplanets (planets outside our solar system) and some of the farthest known galaxies. Recently, Spitzer helped discover the closest known rocky exoplanet to us, named HD219134b, at 21 light-years away.
In fact, Spitzer's exoplanet studies continue to surprise the astronomy community. The telescope wasn't originally designed to study exoplanets, but as luck -- and some creative engineering -- would have it, Spitzer has turned out to be a critical tool in the field, probing the climates and compositions of these exotic worlds. This pioneering work began in 2005, when Spitzer became the first telescope to detect light from an exoplanet.
Other top discoveries from the mission so far include:
 -- Recipe for "comet soup." Spitzer observed the aftermath of the collision between NASA's Deep Impact spacecraft and comet Tempel 1, finding that cometary material in our own solar system resembles that around nearby stars.
-- The largest known ring around Saturn, a wispy, fine structure with 300 times the diameter of Saturn.
-- First exoplanet weather map of temperature variations over the surface of a gas exoplanet. Results suggested the presence of fierce winds.
-- Asteroid and planetary smashups. Spitzer has found evidence for several rocky collisions in other solar systems, including one thought to involve two large asteroids.
-- The hidden lairs of newborn stars. Spitzer's infrared images have provided unprecedented views into the hidden cradles where young stars grow up, revolutionizing our understanding of stellar birth.
-- Buckyballs in space. Buckyballs are soccer-ball-shaped carbon molecules that have important technological applications on Earth.
-- One of the most remote planets known, lying about 13,000 light-years away, deep within our galaxy. Spitzer continues to help in the search for exoplanets using a state-of-the-art method called microlensing.
-- Massive clusters of galaxies. Spitzer has identified many more distant galaxy clusters than were previously known.
-- "Big baby" galaxies. Spitzer and Hubble has found remote galaxies that were much more massive and mature than expected.
JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

quarta-feira, 19 de agosto de 2015

NASA WEB ·Student Satellite Headed To International Space Station

A very special week is about to begin for approximately 30 students from Aalborg University, in Denmark, as their satellite - AAUSAT5 - waits to be launched to the International Space Station. 
A few weeks later, AAUSAT5 will be deployed into orbit around Earth, marking the first ESA student CubeSat mission ever launched from the ISS: the pilot project of ESA's 'Fly Your Satellite from the ISS!' education programme.
AAUSAT5, a CubeSat satellite entirely built by a university team with ESA's support, will reach the ISS aboard the Japanese HTV-5 cargo vehicle, planned to lift off from the Tanegashima Space Center in Japan. It will be accompanied by GomX-3, another ESA CubeSat, designed by Danish professionals.
There may be a possibility, to be confirmed at a later stage, that AAUSAT5 and GomX-3, both Danish satellites, are released to orbit in conjunction with the mission to the ISS of ESA astronaut Andreas Mogensen, the first Danish astronaut ever. Andreas will be on the station for 2 weeks, starting on 2 September.
After deployment, AAUSAT5 will start its technical mission: test, in orbit, an improved version of an automated positioning system. This system is designed to track and identify ships transiting away from coastal areas and in remote areas, thereby creating potential for safer use of new shipping lanes.
"It is by going through the whole process of setting objectives for a space mission, and then designing, building, testing, and operating a spacecraft that can achieve these objectives, that the students acquire an powerful experience in the space sector, while still completing their studies," said Piero Galeone, Head of the Tertiary Education Unit at ESA. "Our mentoring efforts are all aimed at helping the students become more competent and mature for the labour market when the time comes."
Updates regarding the exact HTV-5 launch time will be made available on this website as soon as they are known. Watch the launch on NASA TV and follow the AAUSAT5 mission with us on the ESA Education portal!
Fly Your Satellite! and AAUSAT5
'Fly Your Satellite!', ESA's most thorough educational CubeSat initiative to date, is a programme aimed at offering university student teams the opportunity to gain exemplary engineering and project management experience in designing, building, testing, launching, and operating a small satellite a CubeSat indeed from cradle to grave.
With AAUSAT5, the ESA Education Office is piloting the opportunity to use the International Space Station as a possible means, in addition to conventional rockets, to recurrently deploy student CubeSats into low Earth orbit; this would represent 'Fly Your Satellite from the ISS!', as an extension of the 'Fly Your Satellite!' programme.
ESA is providing the AAUSAT5 team with the launch opportunity on board the HTV-5 launch vehicle and the deployment from the International Space Station free of charge, as well as technical and financial support for the pre-launch activities (for satellite integration and testing, and for the delivery to Houston, US, where the satellite has been integrated with the NanoRacks CubeSat Deployer (NRCSD).

NASA WEB · Bigelow Aerospace and NASA Execute NextSTEP Contract to Study B330 Utilization

Bigelow Aerospace and NASA Execute NextSTEP Contract to Study B330 Utilization.

Dual B330 modules in lunar orbit
NASA has executed a contract with Bigelow Aerospace for the company to develop ambitious human spaceflight missions that leverage its innovative B330 space habitat.
The contract was executed under the Next Space Technologies for Exploration Partnerships ("NextSTEP") Broad Agency Announcement issued by NASA's Advanced Exploration Systems program.
Via its NextSTEP contract, Bigelow Aerospace will demonstrate to NASA how B330 habitats can be used to support safe, affordable, and robust human spaceflight missions to the Moon, Mars, and beyond. As the name indicates, the B330 will provide 330 cubic meters of internal volume and each habitat can support a crew of up to six. Bigelow expandable habitats provide much greater volume than metallic structures, as well as enhanced protection against radiation and physical debris. Moreover, Bigelow habitats are lighter and take up substantially less rocket fairing space, and are far more affordable than traditional, rigid modules. These advantages make the B330 the ideal habitat to implement NASA's beyond low Earth orbit ("LEO") plans and will support the utilization of transportation systems such as the SLS and Orion. Additionally, the B330s, which will initially be deployed and tested in LEO, will be used as private sector space stations that will conduct a wide variety of commercial activities.
"We're eager to work with NASA to show how B330s can support historic human spaceflight missions to the Moon and other destinations in cislunar space while still staying within the bounds of the Agency's existing budget," said Bigelow Aerospace's President and founder, Robert T. Bigelow. "NASA originally conceived of expandable habitats decades ago to perform beyond LEO missions, and we at Bigelow Aerospace look forward to finally bringing that vision to fruition."

NASA WEB · Send Your Name to Mars on NASA's Next Red Planet Mission Mars enthusiasts around the world can participate in NASA's journey to Mars by adding their names to a silicon microchip headed to the Red Planet aboard NASA's InSight Mars lander, scheduled to launch next year.

Send Your Name to Mars on NASA's Next Red Planet Mission
Mars enthusiasts around the world can participate in NASA's journey to Mars by adding their names to a silicon microchip headed to the Red Planet aboard NASA's InSight Mars lander, scheduled to launch next year.
"Our next step in the journey to Mars is another fantastic mission to the surface," said Jim Green, director of planetary science at NASA Headquarters in Washington. "By participating in this opportunity to send your name aboard InSight to the Red Planet, you're showing that you're part of that journey and the future of space exploration."
Submissions will be accepted until Sept. 8. To send your name to Mars aboard InSight, go to:

The fly-your-name opportunity comes with "frequent-flier" points to reflect an individual's personal participation in NASA's journey to Mars, which will span multiple missions and multiple decades. The InSight mission offers the second such opportunity for space exploration fans to collect points by flying their names aboard a NASA mission, with more opportunities to follow.
Last December, the names of 1.38 million people flew on a chip aboard the first flight of NASA's Orion spacecraft, which will carry astronauts to deep space destinations including Mars and an asteroid. After InSight, the next opportunity to earn frequent flier points will be NASA's Exploration Mission-1, the first planned test flight bringing together the Space Launch System rocket and Orion capsule in preparation for human missions to Mars and beyond.
InSight will launch from Vandenberg Air Force Base, California, in March 2016 and land on Mars Sept. 28, 2016. The mission is the first dedicated to the investigation of the deep interior of the planet. It will place the first seismometer directly on the surface of Mars to measure Martian quakes and use seismic waves to learn about the planet's interior. It also will deploy a self-hammering heat probe that will burrow deeper into the ground than any previous device on the Red Planet. These and other InSight investigations will improve our understanding about the formation and evolution of all rocky planets, including Earth.

terça-feira, 11 de agosto de 2015

NASA WEB ·One Decade after Launch, Mars Orbiter Still Going Strong

For Anniversary of Orbiter's Launch: Seasonal Flows in Mars' Valles Marineris
Among the many discoveries by NASA's Mars Reconnaissance Orbiter since the mission was launched on Aug. 12, 2005, are seasonal flows on some steep slopes, possibly shallow seeps of salty water. This July 21, 2015, image from the orbiter's HiRISE camera shows examples within Mars' Valles Marineris. Image credit: NASA/JPL-Caltech/Univ. of Arizona
› Full image and caption
Fast Facts:
› NASA's Mars Reconnaissance Orbiter was launched on Aug. 12, 2005
› MRO returns more data about Mars every week than all other Mars missions combined and supports Mars surface missions
› It has orbited Mars 40,000 times and returned 250 terabits of data so far (as much data as in nearly four months of nonstop high-definition video)
Ten years after launch, NASA's Mars Reconnaissance Orbiter (MRO) has revealed the Red Planet's diversity and activity, returning more data about Mars every week than all six other missions currently active there. And its work is far from over.
The workhorse orbiter now plays a key role in NASA's Journey to Mars planning. Images from the orbiter, revealing details as small as a desk, aid the analysis of potential landing sites for the 2016 InSight lander and Mars 2020 rover. Data from the orbiter will also be used as part of NASA's newly announced process to examine and select candidate sites where humans will first explore the Martian surface in the 2030s.
An Atlas V rocket launched the orbiter on an early Florida morning from Cape Canaveral Air Force Station on Aug. 12, 2005, propelling it on a course toward Mars.
"The most crucial event after launch was orbit insertion on March 10, 2006," said JPL's Dan Johnston, MRO project manager. "The 27-minute burn of the spacecraft's main engines, necessary for orbit capture, was scheduled for completion while the spacecraft was behind Mars, so we had to wait in suspense for confirmation that it went well. It did. As planned, the initial orbit was highly elliptical. Then we had nearly five months of aerobraking -- using controlled friction of more than 400 dips into the upper fringe of the atmosphere -- to shrink the orbit to a nearly circular shape."
MRO's primary science mission began in November 2006 and lasted for one Mars year, equivalent to about two Earth years. The orbiter has used six instruments to examine Mars' surface, subsurface and atmosphere. The spacecraft has been orbiting Mars at an altitude of about 186 miles (300 kilometers) above the Red Planet, passing near the north and south poles about 12 times a day.
"Mars Reconnaissance Orbiter has found evidence of diverse watery environments on early Mars, some more habitable than others," said the mission's project scientist, Rich Zurek of NASA's Jet Propulsion Laboratory, Pasadena, California. "MRO has discovered that Mars' south polar cap holds enough buried carbon-dioxide ice to double the planet's current atmosphere if it warmed. It's caught avalanches and dust storms in action. The spacecraft's longevity has made it possible to study seasonal and longer-term changes over four Martian years. These studies document activity such as moving dunes, freshly excavated impact craters -- some which expose subsurface ice -- and mysterious strips that darken and fade with the seasons and are best explained as brine flows."
Though it has already served longer than planned, the spacecraft could remain a cornerstone of NASA's Mars Exploration Program fleet for years to come.
In addition to continuing to make its own discoveries about Mars, the mission delivers crucial support for surface-based missions. This support includes communication relay service and detailed observations of candidate landing sites for rovers and stationary landers past, present and future.
"Ten years after launch, MRO continues full science and relay operations," said Kevin Gilliland, spacecraft engineer for the mission at Lockheed Martin Space Systems, Denver. "We've kept our operations efficient. We've been able to bring back an astonishing amount of science data -- more than 250 terabits so far. Even after more than 40,000 orbits, the mission remains exciting, with new challenges such as taking close-up images of a passing comet last year and supporting next year's InSight landing."
The InSight mission will place a lander on Mars to investigate the deep interior of the Red Planet for clues about the formation and evolution of all rocky planets, including Earth. A maneuver two weeks ago altered MRO's orbit, as planned, to put it in position to provide communication support for InSight's Sept. 28, 2016, landing.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington. Lockheed Martin built the orbiter and collaborates with JPL to operate it.