Markings Mar Mars

NASA/JPL & Malin Space Science Systems; May 28, 2001; Press Release: "Mars Global Surveyor spots a mid-summer's dust devil"

NASA/JPL & Malin Space Science Systems; May 29, 2001; Press Release: "Probe spots newly formed streaks on Martian slopes"

Mars Global Surveyor (MGS) recently completed its primary mission of imagining Martian features over the course of a Martian year. Now the orbiter has entered the Extended Mission phase, which includes re-imaging the planet in search of changes to the Martian topography. From the early results, it looks like Mars is wowing the Mars Orbiter Camera (MOC) Staff with exciting images of a living planet.

Dust devil tracks across Mars -- NASA/JPL/MSSS

The image here is that of a kilometer high dust devil, a vortex of dust-laden wind, and the 1.5-km, kinked shadow it cast. The dust devil is arrowed in the image as "dust," and the camera was overhead looking straight down. From overhead, this phenomena would usually appear as an oval of dust casting a straight shadow, but this specimen has an obvious twisted appearance. A light-colored line to the left of the dust devil ("track") reveals its direction of travel is to the right -- east in the photo. The color of the line indicates that light colored sand is found beneath a thin layer of dark sand. This area of Mars is called Amazonis Planitia, and the dust devil was imaged on April 10th of this year.

Dust devils are common in arid areas of our planet, such as Arizona. They are caused by air warming above a surface. As the air rises it spins and picks up loose dust and sand. This Martian dust devil occurred at around 2 p.m. local time -- the optimal time for such phenomena to appear on Earth or Mars.

Dark slope streaks in Lycus Sucli --: NASA/JPL/MSSS

The next images are comparison shots, of the rugged Lycus Sulci area, taken on August 2, 1999 and April 27 of this year. Dark lines on the images are the result of dry, fine, bright dust avalanching and revealing a darker surface underneath. The images suggest that one avalanche occurs per kilometer of slope each Martian year.

North is toward the top of the images and sunlight is from the left. Older streaks can be seen in the 1999 photo, with new streaks arrowed on the more recent image.  Arrowed streaks are on the order of 500-m or more in length.  These avalanche streaks are most common in the dust-covered Martian regions of Tharsis, Arabia, and Elysium.

Potentially Hazardous Asteroid Caught By Radar

SpaceDaily.com; May 30, 2001; Asteroids: "JPL Radar Scans Asteroid Moon During Earth Flyby"

1999 KW4 is binary -- NASA

The ghostly image illustrating this article is a radar image of a binary asteroid that swept past Earth on May 25, at a distance of only 5-million km. Known as 1999 KW4, it is the third near-Earth asteroid that radar studies have revealed to be binary. The looping trail is the smaller component passing over the larger primary body in a time-exposure.  Images were made with the 70-meter Goldstone antenna, in California's Mojave Desert. The series of images made by the Goldstone dish required 8-hours of tracking each day for a week. Close-up studies of each component were made with the more powerful, but less steerable, Arecibo radio telescope in Puerto Rico.

The primary member of the pair was found to be a spheroid of 1.2-km diameter and the smaller just a third that size. The companion object takes about 16-hours to orbit the primary. Mass and density estimates will be generated from the radar data obtained from the pass.

Doing a radar study of the pair provides much more than an interesting picture. 1999 KW4 is of special interest to researchers because its elongated orbit takes it closer to the Sun than Mercury and the path is highly inclined to that of the Earth. These are the hallmarks of a cometary orbit: the asteroid may be a comet nucleus that lost its volatiles. The close pass also allows us to study the orbit more closely. "The asteroid pair 1999 KW4 is classified a Potentially Hazardous Asteroid because eventually its path through space could intersect Earth. However, the radar measurements, which are accurate to 15-meters (about 49-feet), indicate there is no significant chance of 1999 KW4 colliding with Earth for at least a thousand years," said Jon Giorgini, a radar team member from JPL.

Only a few percent of the near-Earth asteroids are thought to be binary, and theorists don't yet understand how asteroid moons evolved. Data from radar surveys will add to the knowledge base concerning these objects and help devise such a theory. Dr. Steven Ostro of NASA's Jet Propulsion Laboratory is the leader of the radar mapping team: "Robotic spacecraft, and eventually people, are destined to go to such objects someday, either for defense against one of them, to exploit mineral resources, to satisfy our curiosity about what they're like close-up or simply for the adventure of exploring a diminutive double world."

Wait. Stop. What's that Sound?

Los Alamos National Laboratory; May 27, 2001; Press Release: "Listeners for nuclear tests hear big meteoroids"

On August 25 of last year, a large meteor collided with the Earth's atmosphere. Though only 6-feet in diameter, it lit the sky off the coast of Acapulco, Mexico, as it broke apart many miles above the Pacific Ocean. The pressure wave from the event was the equivalent to that of an explosion of 2,000 to 3,000 tons of TNT. This last April 23, a larger meteor, of at least 10-foot diameter, again flashed over the Pacific, hundreds of miles west of the northern Baja California region of Mexico. Its pressure wave was the equivalent of a 6,000 to 8,000 or more tons of TNT and must have been a fiery sight. Though the pressure wave numbers indicate a tremendous destructive potential, meteors of this size -- also known as bolides -- break-up in the outer atmosphere and rain few if any recognizable fragments onto the surface.

Yet, nobody reported seeing these brilliant lights in the sky. So if a meteor falls through the sky and nobody sees it, how do you know it fell at all? The answer: by hearing it. Researchers at Los Alamos National Labs used an infrasonic acoustic system, designed to detect clandestine nuclear weapons tests, to triangulate the sound-wave signature of the bolides and determine their size and location.

There are four arrays in the U.S. dedicated to detecting the sound waves of nuclear explosions, and five more are part of an overseas international monitoring effort. The time-delay between the arrivals of acoustic signals at the arrays is used to triangulate the location of the event. Because of the size of the Earth, the sound waves may reach the arrays from minutes to hours after the event. So don't count on the arrays for early warning of a bolide. Sound frequency data is used to determine the explosive power of the event; for bolides, this can be translated into a physical size estimate.

These are not isolated events. The monitoring arrays detect a number of large meteors every year. Los Alamos researcher Doug ReVelle states of the April event: "That meteor was one of the five brightest meteors that have ever been recorded, it was a very large bolide."

Meteor detections, far from being a distraction to the primary mission of the arrays, help fine-tune the technology. This is done by calibrating the array data with observations of the event from space satellites.

Won't You Bring Back, Bring Back, Bring Back My Pioneer to Me!

BBC.co.uk; May 15, 2001; Sci/Tech: "Mystery force tugs distant probes"

CNN.com; May 21, 2001; Space: "Puzzling hyper-gravity proves weighty mystery"

Aero.org; Oct. 26, 1998; Press Release: "Aerospace Analysis Helps Confirm Unexplained 'Pull' on Spacecraft"

Pioneer 10 at Jupiter stamp.  U.S.P.S.

On the heels of its triumphant contact with Earth (NewsNotes: 05.01.01 It Keeps on Ticking!), Pioneer 10's voyage is a central topic in a report that may topple accepted theories of gravity. Launched in 1972, Pioneer 10 completed its primary mission when it swept past Jupiter in 1973. For almost 30-years it has been returning information about our outer Solar System. Funding for the probe continued in later years when it was tasked with detecting the heliopause, where particles streaming out from the Sun encounter particles from interstellar space. As of this writing it has not crossed that boundary. In order to fund regular radio contacts with the probe, though the cash-strapped late-90's, Pioneer was used as a training craft for controllers and then employed in a study for extracting data from faint radio signals. As its radio voice grew weak with distance, each contact with Earth was regarded as possibly the last.

Amazingly, the new revelation in physics made possible by Pioneer is not derived from the measurement data returned by the spacecraft: the data signal itself contains the clue. Pioneer's motion relative to Earth-based receiving stations causes its radio signal to undergo a Doppler shift. Since 1980 this shift has been used to calculate Pioneer's relative motion with great detail. This data, when compensated for the motion of the Earth, indicates that a force, whose magnitude points in the direction of the Sun, is impeding Pioneer 10's progress. Because the force is billions of times smaller than that of gravity at the Earth's surface, it took years of monitoring to determine that the effect was not some random error.

When the tracking discrepancy was first reported in 1998, possible forces on the craft from such things as fuel leaks, radiation pressure, and unseen gravitational bodies had not been ruled -- now they have. The validity of the Pioneer 10 data is bolstered by similar studies of signal data from Pioneer 11, which ceased communicating with Earth in 1995. That sister craft experiences the same force as it exited the solar system in the direction opposite of Pioneer 10 -- a distance of 14-billion miles separates them.

Is this a new force or previously unknown deviation in a known force?  Dr. John Anderson, of the Jet Propulsion Laboratory, has been examining this anomaly for years. "It is almost as if the probes are not behaving according to the known law of gravity," he said. "We've been working on this problem for several years, and we have accounted for everything we could think of."  This brings up the possibility that Pioneer's predicament may indicate a deviation in the force of gravity across large distances. If ever confirmed, this would reverberate throughout the physics community and cast into doubt assumptions made under the current understanding of gravity. Others counter that a gravity deviation would affect the orbits of the planets, which show no deviation.

Signal data from other space probes have been examined for clues concerning the anomaly. There are indications that the Galileo craft orbiting Jupiter and the Sun-orbiting Ulysses probe also experience the force. Voyagers 1 and 2, heading out of our system with the Pioneers, cannot be employed in detecting the anomaly due to technical reasons. Are the Pioneer spacecraft trajectory anomalies the result of some unknown force generated by those vehicles? Since we can't bring any of those space probes back to Earth for examination, the anomaly may remain an open question for a long while.