Probes Break the Law

Mystery Force Tugs Distant Probes

We can lick gravity, but sometimes the paperwork is overwhelming.

- Wernher von Braun

It's a good thing we have gravity, or else when birds died they'd just stay right up there.
Hunters would be all confused.

- Steven Wright

by Dr David Whitehouse

An unexplained force is pulling on distant spacecraft. Researchers have come to this conclusion after a thorough analysis of the deep-space probes' trajectories. It could be just a tiny unnoticed effect in the spacecraft themselves, but scientists warn it could also be the first hint that modifications need to be made to our understanding of the force of gravity.

"It is almost as if the probes are not behaving according to the known law of gravity," said Dr John Anderson, of the American space agency's (NASA) Jet Propulsion Laboratory, and lead scientist on the study. He said: "We've been working on this problem for several years, and we have accounted for everything we could think of."

The unexplained force appears to be acting on four deep-space probes scattered around the solar system. Pioneer 10 was launched towards the outer planets in 1972. It is now well beyond Jupiter but still in radio contact with the earth. By studying the Doppler shift (the "stretching") of the radio signals from the probe, scientists have been able to calculate how fast the craft is travelling. Since 1980, its trajectory has been mapped in very great detail. The puzzle is that Pioneer 10 is slowing more quickly than it should. It was initially suggested that this might be due to the force from a tiny gas leak or that it was being pulled off course by the gravity of an unseen solar system object.

The mystery deepened further when an analysis of the trajectory being followed by its sister spacecraft, Pioneer 11, launched in 1973, showed that it too was being subjected to the same mysterious effect. But Pioneer 11 is on the opposite side of the solar system from Pioneer 10, about 22 billion km (about 14 billion miles) away. This means the effect cannot be the gravitational effect of some unseen body.

Add to all this hints that the same unexplained effect might have been acting on the Galileo spacecraft on its journey to Jupiter, and the Ulysses spaceprobe that is circling the sun, and you have a Solar System-wide puzzle.

In a report soon to be published in a major astronomical journal, Dr Anderson and colleagues have carried out an impressive study of the state of the Pioneer spacecraft and all the tiny forces to which they could be subjected. "Our analysis strongly suggests that it is difficult to understand how any of these mechanisms can explain the magnitude of the observed behaviour of the Pioneer anomaly," the team says.

It has been suggested that the spacecraft tracking data have shown a deviation in the force of gravity that is apparent only across vast distances. It has also been pointed out that the strength of the effect seems to be related to two of the Universe's physical constants: the speed of light and the speed of the expansion of the universe.

But others have dismissed this as being too fanciful, arguing that if the Pioneer anomaly was really indicative of a change in our understanding of gravity, then it would be apparent in the orbits of the planets around the sun - which it is not. The effect is as yet unexplained and with all four affected probes never to return to the earth for analysis, it may well remain that way.

Dr David Whitehouse is the science editor for the BBC News Online

Source: news.bbc.co.uk Tuesday 15 May 2001

A New Idea

Loop Quantum Cosmology (LQC) is the first tangible application of a theory called loop quantum gravity. It combines Einstein's theory of gravity with quantum mechanics.

The Big Bang requires a singularity where gravity, temperature and the density of the universe become infinite. General relativity fails to describe what happens because then because it can't cope with infinity. But assume the fabric of space-time is instead woven from loops of gravitational field lines. Zoom out far enough and space appears smooth and unbroken - but a close look reveals that space comes in indivisible chunks, or quanta, 10^-35 square metres in size. If LQC turns out to be correct, our universe emerged from a pre-existing universe that first expanded (like ours) before it contracted due to gravity. As all its matter ultimately squeezed into a microscopic volume, it neared the so-called Planck density, 5.1 × 1,096 kilograms per cubic metre.

Theory forbids reaching this density because an extraordinary repulsive force develops in the fabric of space-time at densities equivalent to compressing a trillion solar masses down to the size of a proton. At this point, the quanta can't be squeezed any more. Their outward force overcomes gravity causing the universe to rebound and keep expanding because of inertia.

But gravity slows it.

If proven - and LQC is is ready to make testable predictions - the big bang will give way to a big bounce and we will finally know the quantum structure of space-time. Instead of a universe that emerged from a point of infinite density, we will have one that recycles, possibly through an eternal series of expansions and contractions, with no beginning and no end.

Source: newscientist.com

We're a Long Way From Home...

The existence of the Sagittarius Dwarf galaxy was unknown until this galaxy nearest the Milky Way was discovered by British astronomers in 1994. The fact that the Milky Way is seen in the sky at an angle has always puzzled astronomers. We ought to be oriented to the galaxy's ecliptic, with the planets aligned around our sun in the same angle as our sun aligns with the Milky Way. Instead, the odd angle suggests an influence by some other system. This is an animation of our galaxy being eaten by the Milky Way.

Click to Play

We now know what it is - we actually belong to the Sagittarius Dwarf galaxy. The outer parts of the Milky Way were stolen from Sagittarius as the gravitational force of the Milky Way nibble away at it. This may be the real reason for global warming since the higher Milky Way energy levels are almost certain to cause our sun to burn hotter and emit higher energies. Indeed, temperatures have been seen to rise on virtually all planets in our system, quite apart from local greenhouse gases. We have now reached the higher energy region of the massive spiral arm - we have been adopted by a new, stronger and more powerful system and can expect changes on almost every level of energy...

Source: viewzone.com source of animation astsun.astro.virginia.edu

Sounds of Saturn

Saturn is a source of intense radio emissions. The radio waves are closely related to the auroras near the poles of the planet. These auroras are similar to earth's northern and southern lights. The Cassini spacecraft began detecting these radio emissions in April 2002 when Cassini was 2.5 astronomical units from the planet using the Cassini Radio and Plasma Wave Science (RPWS) instrument. The RPWS has now provided the first high resolution observations of these emissions that show an amazing array of variations in frequency and time. The complex radio spectrum with rising and falling tones is very similar to earth's auroral radio emissions. These structures indicate that there are numerous small radio sources moving along magnetic field lines threading the auroral region.

In the second example, it appears as though the three rising tones are launched from the more slowly varying narrowband emission. If this is the case, it represents a very complicated interaction between waves in Saturn's radio source region, but one which has also been observed at earth!

The sound of the radio emissions can be heard by clicking the buttons below (the sounds are in mp3 format). Time on the top recording has been compressed such that 73 seconds corresponds to 27 minutes, or, the recording is at 22x real time. Since the frequencies of these emissions are well above the audio frequency range, they have been shifted downward by a factor of 44.

Time on the second example has been compressed such that 13 seconds corresponds to 27 seconds, or, about 2x real time. Since the frequencies of these emissions are well above the audio frequency range, they have been shifted them downward by a factor of 260.

Bill Kurth
RPWS Deputy Principal Investigator

Sources: cassini.physics.uiowa.edu/space-audio/cassini/SKR1 and cassini.physics.uiowa.edu/space-audio/cassini/SKR2 25-Jul-2005

Cassini Reveals Saturn's Eerie-Sounding Radio Emissions

by Harvey Leifert

Washington - Saturn's radio emissions could be mistaken for a Halloween sound track. That is how University of Iowa researchers Bill Kurth and Don Gurnett describe their recent findings, published 23 July in the journal Geophysical Research Letters. Their research investigated sounds that are not just eerie, but also descriptive of a phenomenon similar to earth's northern lights. The study was based on data from the Cassini spacecraft's radio and plasma wave science instrument, which was built at the University of Iowa under Gurnett's direction.

"All of the structures we observe in Saturn's radio spectrum are giving us clues about what might be going on in the source of the radio emissions above Saturn's auroras," says Kurth. "We believe that the changing frequencies are related to tiny radio sources moving up and down along Saturn's magnetic field lines." The radio emissions, called Saturn kilometric radiation, are generated along with Saturn's auroras, or northern and southern lights. The Cassini instrument has provided new information on the spectrum and the variability of the radio emissions, thanks to the higher resolution of the instrument, as compared to that on the earlier Voyager spacecraft. These high-resolution measurements allow scientists to convert the radio waves into audio recordings by shifting the frequencies down into the audio frequency range.

The terrestrial cousins of Saturn's radio emissions were first reported in 1979 by Gurnett, who used an instrument onboard the International sun-earth Explorer spacecraft in earth orbit. Kurth says that despite their best efforts, scientists still have not agreed on a theory to fully explain the phenomenon. He adds that they will get another chance to solve the radio emission puzzle beginning in mid-2008, when Cassini will fly close to, or possibly even through, the source region at Saturn.

Commenting on the new observations, Gurnett says, "It is amazing that the radio emissions from Earth and Saturn sound so similar."

Harvey Leifert
hleifert@agu.org
American Geophysical Union

The research at the University of Iowa was funded by NASA.

Save the Earth

by Mark A Garlick

Delaying our planet's ultimate demise - by shifting its orbit

One billion years - that's about all the time we have until the increasing luminosity of the ageing sun cooks our planet to near death. But it does not have to be this way. Researchers argue that gradually moving Earth farther from the sun is possible.

Since the sun formed 4.6 billion years ago, it has steadily grown and gotten brighter. Already it shines about 30 to 40% brighter than it did when it first entered the main sequence, its current long-Iived period of stability. In about one billion years the sun will be 10% more luminous than it is now - more than adequate to make land-based life difficult or even impossible.

A team led by Donald G Korycansky of the University of California at Santa Cruz has developed an ambitious yet feasible plan that could add another six billion years to our planet's sell-by date. The process is an unusual application of the well-known gravitational slingshot. As a spacecraft closes in on a planet, gravity accelerates the probe, and it shoots away with added energy. That extra energy does not come free, though: the planet suffers equal and opposite changes in energy and momentum.

In the same way, the team's paper, published in the March Astrophysics and Space Science, shows how Earth's orbit can be increased very slightly if a suitable asteroid (or any object about 100 kilometres across and weighing about 1,016 metric tons) can be made to fly in front of Earth as it moves in its orbit. In doing so, the asteroid imparts some of its orbital energy to Earth, shifting it to a slightly larger orbit. The orbit of the asteroid is engineered such that, after its flyby of Earth, it heads toward Jupiter or Saturn, where in the reverse process it picks up the orbital energy it lost to Earth. Then, when the asteroid reaches its farthest distance from the sun, a slight course correction is applied - by, say, firing engines on the asteroid using fuel manufactured from materials mined there - sending it once more toward Earth.

Korycansky and his collaborators calculate that for Earth to enjoy the same intensity of sunlight it does now, our planet would have to be nudged outward about once every 6,000 years, on the average, for the entire remaining main-sequence lifetime of the sun. In 6.2 billion years Earth would be just beyond the current orbit of Mars. The scenario sounds like science fiction, but it actually uses technology that is mere decades away from being reality.

Ambitious though the scheme is, it is no solution when the sun encounters its fate - as a cool, dim white dwarf. At the very end, escaping to another star system is ultimately the only option.

Drawbacks

Sending a giant rock toward Earth every 6,000 years has its dangers:

	Collision - The asteroid could hit Earth, rather than flying by it.
	Orbital Destabilisation - The change in Earth's orbit could disturb the motions of the other planets.
	Loss of the Moon - Most likely, the moon would be stripped away from Earth unless some additional energy-expensive shepherding were arranged. The moon helps to stabilise Earth's axial tilt, and its absence could radically upset our planet's climate.

Mark A Garlick, a former astronomer, is a writer and artist based in Brighton, England

Source: Scientific American June 2001

Can Matter Travel at Light Speed? Not Quite

Bejing - Unless the basic principles of the universe discovered by Einstein are proven wrong, which hardly any physicist would expect, the short answer to the question "can matter travel at light speed" is "no." But astrophysicists have recently discovered gas and dust in two distant exploding stars moving at 99.9997% of the speed of light - about 2,000 mph too slow to qualify.

When a super-massive star explodes, sometimes called a hypernova, it flings gas and dust into space with amazing energy, in effect causing it to outshine most objects in the nearby universe. In the recently discovered explosions, about 200 earth's worth of material, in the form of stellar gas and dust, was propelled near light-speed for a few moments. Such a large amount of matter moving so quickly may seem extremely close to light speed, but the energy required to move even a little faster is nearly infinite. To understand this, Einstein’s famous E=mc² equation is useful. There's a more complex version that accounts for velocity

(v): E=γmc² where γ=1/(√ 1-v²/c²)

If the equation looks confusing, here's a summary: The faster an object moves, an exponentially larger amount of energy is needed to speed it up, which is why travelling at light speed requires an infinite amount of energy.

Source: news.xinhuanet.com 15 June 2007

Milky Way

In this artists rendering released by the University of Wisconsin, the Milky Way has a definitive bar feature -
some 27,000 light years in length - that distinguishes it from most spiral galaxies. (Photo by University of Wisconsin)

Crab Nebula

The Crab Pulsar, a city-sized, magnetised neutron star spinning 30 times a second,
lies at the center of this composite image of the inner region of the well-known Crab Nebula.

This spectacular picture combines optical data (red) from the Hubble Space Telescope and x-ray images (blue) from the Chandra Observatory. Like a cosmic dynamo the pulsar powers the x-ray and optical emission from the nebula, accelerating charged particles and producing the eerie, glowing x-ray jets. Ring-like structures are x-ray emitting regions where the high energy particles slam into the nebular material. The innermost ring is about a light-year across. With more mass than the sun and the density of an atomic nucleus, the spinning pulsar is the collapsed core of a massive star that exploded, while the nebula is the expanding remnant of the star's outer layers. The supernova explosion was witnessed in the year 1054AD.

Click to play

In the summer of 1054AD, Chinese astronomers reported that a star in the constellation of Taurus suddenly became as bright as the full moon. Fading slowly, it remained visible for over a year. The core of the star collapsed to form a rotating neutron star or pulsar, one of the most exotic objects known to modern astronomers. Like a cosmic lighthouse, the rotating Crab pulsar generates beams of radio, visible, x-ray and gamma-ray energy which, as the name suggests, produce pulses as they sweep across our view. Using a stunning series of visible light images taken with the Hubble Space Telescope (HST) in 1995, astronomers have discovered spectacular pulsar powered motions within the Crab nebula. Highlights of this HST Crab "movie" show wisps of material moving away from the pulsar at half the speed of light, a scintillating halo, and an intense knot of emission dancing, sprite-like, above the pulsar's pole. Only 10 kilometers wide but more massive than the sun, the pulsar's energy drives the dynamics and emission of the nebula itself which is more than 10 light-years across.

Source: antwrp.gsfc.nasa.gov, hubblesite.org, J Hester (ASU) et al, CXC, HST, NASA