Anatomy of an Asteroid Investigation
30 Oct 2003
(Source: The Planetary Society)
Scientists Find an 'Asteroid' is Apollo 12 Debris
Anatomy of an Asteroid Investigation
By A.J.S. Rayl
The Planetary Society
30 October 2003
Heaven and Earth are about to collide . . . An asteroid the size of Texas is speeding directly toward Earth at 22,000 miles per hour and NASA's executive director has only one option -- to send up a crew to destroy the asteroid . . .
It was only a movie. But Armageddon and other films of its ilk back in the late 1990s presented an image of asteroid fear and injected it into a public consciousness that ebbs and flows today.
The more our ability to 'see' in space has improved and the more missions we send into space, the more we know there are all kinds of things flying around out there that could someday, somehow, somewhere drop in on Earth. That knowledge -- along with evidence of past meteor and asteroid impacts on Earth and other planets, and those thought-provoking Hollywood movies - has fueled public intrigue and concern about anything out of the ordinary that might be orbiting our world.
Just a glance at a map showing the space debris around our planet reveals that we are literally encircled in junk, and the prospects for disaster in imaginative minds can loom large. In reality, however, the general public can rest assured about one thing: all kinds of people are keeping close watch over the heavens above.
Every few weeks, automated asteroid surveys scan the skies looking for any errant space rocks or anything else that's out of the ordinary and moves. Nothing of any interest, no matter what it might ultimately turn out to be -- an asteroid or a piece of space junk, or even an extraterrestrial spacecraft -- is going to get by this global group of astronomers and researchers who represent all variety of space science fields.
Virtually every object that dares venture near our planetary airspace is detected, analyzed, and scrutinized with multiple methods, almost always from multiple observatories. In the vast majority of cases, the objects turn out to be rather docile and non-threatening.
A case in point is the mysterious object found in orbit around the Earth (about twice as far away as the Moon) by Hong Kong born, Canadian amateur astronomer Bill Yeung in September 2002. Known as J002E3, Yeung had reason to believe it was an authentic asteroid and a group of scientists thought it was interesting enough to take notice and investigate the object every astronomical which way. How they finally came to the almost unequivocal conclusion that it was actually the third stage of the Saturn IV booster that launched Apollo 12 in 1969 is a tale that unfolds something like a modern day detective story, illustrating along the way the kind of time and effort that go into identifying any thing strange that may orbit our way.
It all started that September day a little more than a year ago, while Yeung was reviewing images of the constellation Pisces taken at the Desert Wanderer Observatory in El Centro, California. Suddenly, he detected a "relatively bright, fast-mover," and thought it might be a near Earth asteroid.
The PinPoint software he was using to analyze the images -- which is designed to detect moving objects in starfields -- identified and labeled the object J002E3, reporting a magnitude of 16.7. Convinced it was an authentic find, Yeung sent the astrometry in to be posted on the NEO Confirmation Page hosted by the Minor Planet Center (MPC).
The Minor Planet Center (MPC) - which operates in the[Image] Harvard-Smithsonian Astrophysical Observatory under the auspices of the International Astronomical Union (IAU) -- is responsible for the collection, checking, and dissemination of astrometric observations and orbits for asteroids or minor planets and comets.
Yeung's belief that it might be an asteroid was certainly reasonable. The automated asteroid surveys had no sign of this object in previous months, and yet there clearly was something orbiting around out there. Whatever it was it was as bright as a 30-meter wide space rock and it seemed to be moving about as fast as an asteroid should move.
Object J002E3, as the story goes, hit the NEO Confirmation Page within the hour. A couple of days later, after the object had been re-observed and found again to be orbiting the Earth, it caught the attention of scientists from various fields within the realm of astronomy and space science -- including orbital engineers Steve Chesley and Paul Chodas from the Jet Propulsion Laboratory (JPL); astronomers Rob Whiteley and Carl Hergenrother, with the Lunar and Planetary Laboratory at the University of Arizona; planetary astronomers Andy Rivkin and Richard Binzel of the Massachusetts Institute of Technology (MIT); and space debris specialists Kira Jorgensen and Faith Vilas from NASA's Johnson Space Center.
During the ensuing weeks, these scientists, along with other interested astronomers, looked at and measured the object in just about every conceivable way, logging some 1200 observations from September 2002 to May 2003 at more than 25 observatories.
The sleuthing began at JPL with Chesley and Chodas calculating the orbit of the object. "We didn't know what it was at the time," remembers Chesley, senior engineer in the solar systems dynamics group in the Navigation and Mission Design Division at the JPL. "Everybody assumed it was a spacecraft, but we couldn't figure out what it could possibly be out that far."
Through their calculations, Chesley and Chodas - who frequently to the asteroid database -- quickly discovered that J002E3 was on a large 48-day orbit around the Earth, unlike most asteroid orbits that only briefly pass near the Earth on their orbits about the Sun. "It was looping around Earth once every 48 days or so, coming as close to our planet as the Moon and ranging as far away as two lunar distances," according to Chodas, an expert in planetary motion.
"Part of the problem -- and one of the strongest arguments for J002E3 being manmade -- is that we could see the effect of solar radiation pressure and non-gravitational acceleration. If this were an asteroid it would not be following this particular path," Chesley explains.
In other words, space debris and asteroids behave differently and since this object was not exactly behaving like an asteroid, by simple deduction it must be something manmade. As their orbital research continued, Chesley and Choda were confident in that early hypothesis.
Within a matter of days, the object was taken off the NEO Confirmation page, the investigation turned to manmade objects.
So what was it?
The Apollo Saturn-IV boosters (S-IVs) were, according to Chesley, "the most obvious explanation from the start." Postulating that scientifically, however, would require much more proof.
"When we first discovered this object, we took a look at where it had come from [by studying the object's past motion] and where it was going [by studying the object's future orbit]," explains Chesley, who presented a talk on J002E3 at the Australian Minor Planet Workshop last summer. "With a week or two worth of data -- we could already see that it had been captured by the Earth-Moon system in early 2002. It also became clear that it was going to be ejected from the Earth-Moon system in early 2003."
Chesley and Chodas considered current space missions, for about a minute. "There are very few active missions orbiting the Earth beyond the lunar distance, and the few potential candidates were easily ruledout," offers Chesley.
From an asteroid to manmade
With the Chesley-Chodas orbit information, Rob Whiteley and Carl Hergenrother spent Sept. 12 and 13 taking photometric observations from the Steward Observatory 61-inch telescope near Mt. Bigelow, north of Tucson, Arizona. They found that J002E3 had "a very fast rotation rate and a possible pole-on orientation," according to space debris specialist Kira Jorgensen, who had been discussing analyzing NEOs with Whiteley when this object was found.
In fact, the spectrum of sunlight reflected from the object that Whiteley and Hergenrother measured suggested that it had different colors than an asteroid. "The colors were consistent with . . . titanium dioxide paint -- the type of paint used on Apollo moon rockets 30 years ago," according to Hergenrother. That was the first direct evidence that the newly discovered object orbiting Earth may actually have been debris from one of the Apollo moon launches more than 30 years ago.
"Rob and Carl were able to get the initial visible measurements, and what at that point we thought was the light curve, which showed a 63-second spin period, and how the object varies over a certain amount of time," offers Jorgensen. "We still are unsure if the number Whiteley obtained is the actual rotation rate. Asteroids and human-made objects have different variations in their light curves. This fact, however, is just evolving and infant in its studies. What we still wanted to get was visible observations of what we believed to be the full rotation of the object based on the spin rate calculations."
Enter Rivkin and Binzel. Using the spin rate calculations from Whiteley, the MIT team took two nights of spectral observations of J002E3, at multiples of 63 seconds, at the NASA Infrared Telescope Facility (IRTF), located atop Hawaii's Mauna Kea. The infrared data measured what they believe was the full rotation of J002E3 on a different wavelength.
"The spin-rate and the IRTF observations also indicated that this object was not a 'normal' asteroid, the team wrote on a poster * presented at the Division for Planetary Sciences meeting of the American Astronomical Society meeting held in August. Observations from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS), conducted by Binzel, Rivkin, and others at MIT, revealed that the shape and slop of J002E3 did not match any of the so-called "regular" asteroids.
Past that, Rivkin and Binzel's IRTF data also correlated well with -- white titanium dioxide paint.
Awash in white paint
Meanwhile at JSC, Jorgensen had been conducting materials analyses and was soon comparing Rivkin's and Binzel's infrared data with the infrared data on spacecraft white paint available in NASA's laboratory.
The IRTF observations, she found, compared similarly with laboratory samples of flown spacecraft materials. "The absorption features in the infrared matched very well with laboratory white paint, so we figured either the asteroid is covered in white paint -- the likelihood of which is very slim, or it's part of a spacecraft," she explains. "That's how we were able to say that it's definitely manmade."
Around the same time at JPL, Chesley and Chodas continued unraveling more of J002E3's orbital history by conducting a number of computer simulations of the object's trajectory. "Once we had enough data, we realized that it was just passing through the Earth-Moon system in 2002 and 2003 -- this was a temporary capture, and then it was going on its way," Chesley says.
They also traced the motion of J002E3 backwards in time to find out where it had been. "We found out that it had been captured at some time in the early 1970s and was ejected from the Earth-Moon system in 1971," says Chesley. "That was an important clue pointing to Apollo." In other words, that orbital data indicated that it could be a piece of debris from a rocket launched back in the late 1960s, early 1970.
Apollo 14, as history shows, launched in January 1971, and according to Chodas' calculation J002E3 broke out of Earth orbit in March 1971. There was only one problem with that hypothesis: NASA had accounted for all of the major pieces of that particular spacecraft.
"The Apollo missions were launching at that time, but we knew exactly where the stages from those missions were - at least most of them," says Chesley. "Apollos 8 through 17 had sent their Saturn IV boosters (S-IVB) out past Earth orbit and Apollo 13 through 17 had confirmed that their upper stages had hit the Moon. So we knew it couldn't be one of those, and Apollos 8 through 11 were confirmed to go into orbit about the Sun, escaping the Earth-Moon system before late 1969. That left Apollo 12."
Back at JSC, Jorgensen had created a model of the Apollo rocket body for additional comparisons. "I took the same materials that went into the Apollo 12 rocket body and made a model cylinder that was of the same dimensions and painted the same as Apollo had been, to match the two as best as I could," she explains.
Within a couple of weeks, her comparisons were complete. The observations of J002E3 showed a "strong correlation" of absorption features to a combination of human-made materials including mostly white paint, black paint, and aluminum.
Jorgensen then went on to validate the IRTF observations of J002E3 with observations at the Air Force Maui Optical and Supercomputing site (AMOS), as well as comparing both sets of observations with previous data on spacecraft launched in 1965 and in 1981. "The comparisons of the visible and the near-infrared observations of J002E3 taken from IRTF and AMOS matched well with the observations of a rocket body launched in 1965 and not those of one launched in 1981," says Jorgensen. "This may indicate that the two objects, the 1965 rocket body and J002E3, have spent similar time in the space environment [although] they are not in the same trajectory."
Apollo 12, where are you?
When Apollo 12 launched in November 1969, the mission team programmed the S-IVB to go into orbit around the Sun, but an error occurred during the maneuver. The crew had jettisoned the rocket body on 15 November 1969 when it was almost out of fuel. Once the astronauts were safely on their way, ground controllers ignited the S-IVB's engine to send it into a Sun-centered orbit, but the burn, for whatever reasons, went on too long and instead of circling the Sun the third stage entered a barely stable orbit around Earth and Moon. In essence, says Chesley, "(I)t didn't get the right kick from the Moon, so that thing was lost." Until a year ago last September, that is.
After the failed injection in 1969, Apollo 12's S-IVB "limped" around the Earth-Moon system for a year and a half, Chesley adds. "Eventually it was kicked out in early 1971. Then, for the next 30 years or so, it circulated around the Sun in an orbit very much like the Earth, until last year when it lapped the Earth and was captured again. It didn't stay for long this time. After six rotations in fact the debris was on its way out of Earth orbit last summer. "It is a little hard to say exactly at what point it 'escaped' since it left the Earth-Moon vicinity over a period of months," Chelsey explains.
Further orbital research revealed the Apollo 12 S-IVB rocket body was last seen in an orbit "almost identical to the one in which J002E3 was when Bill Yeung had found it," adds Chesley. "The energy is the same and everything was right for J002E3 to be Apollo 12."
By late last Fall, all the data -- the orbital information, various observations, spectral data, and model comparisons -- were pointing to object J002E3 being Apollo 12. But the team still didn't have the 'smoking gun' proof it needed to say unequivocally that it definitely was/is Apollo 12. So, officially, they concluded: J002E3 is "a human-made object from an Apollo rocket upper stage, most likely Apollo 12."
That was good enough for some media, as headlines turned belief into fact, reporting that the 'asteroid' was Apollo 12 debris.
"There's no question that it is some kind of artificial object," reiterates Chesley. "The other question -- is it Apollo 12's third stage -- we can't think of any other explanation. But, we also can't be sure. The problem is that we can't find an orbit that allows J002E3 to pass near the Moon in November 1969, and, thus, we cannot tie the two objects directly together by a single trajectory," he explains. "We think we know why: we don't know very well what solar radiation pressure is doing to the orbit."
First known case of temporary satellite capture
In all likelihood J002E3 is probably the Apollo 12 rocket body, but no matter what it turns out to be, this much is certain: J002E3 is the first known case of temporary satellite capture for Earth. Such events are "well documented for Jupiter, with comets," says Chesley. But for terra firma, the event was novel.
So, will Earth 'capture' the Apollo 12 rocket body again?
"We don't know what the future holds," Chesley says matter-of-factly. Currently, the rocket body is following an anarchistic path. "This thing is really a wanderer now in interplanetary space," he continues. "Once it gets tangled up in the Earth-Moon system, it follows this chaotic wandering trajectory, sweeping out essentially into large volumes of space, and moving so slowly that it could at some point in the future hit the Earth."
That may sound a lot worse than meant. You see, if that piece of Apollo 12 does come back around on an impact trajectory for Earth, it really won't present much danger.
"Although pieces of debris actually do reenter often, this particular Apollo 12 debris is not really an issue," says Jorgensen. Usually, by the time any pieces of space debris come back in, there's not much left, she says. "Also, NASA does do reentry assessments on spacecraft that have been launched now that they realize space debris could pose a problem, so if it's going to come back in, they know what kind of pieces are going to survive. The main thing to remember is that 70% of the Earth is covered in water. The chances of it landing on land are slim to begin with."
Chesley agrees: "Compared to asteroids which have one in a million kind of impact probabilities, even the dangerous ones -- J002E3 has a very high probability of impact over say the next 1000 years either into the Earth or Moon," he elaborates. "Now, that's over thousands of years, and we don't even know the next time it's going to re-visit the Earth. We can see that it will not get captured at the next opportunity (when it next laps Earth), but we cannot be so sure about the second opportunity, about 40 years from now."
Still, even if the Apollo 12 rocket body did come back on a collision course with Earth, it probably wouldn't even make a splash - or dent. "The re-entry would be less exciting, and less substantial than SkyLab," says Chesley, which re-entered over Australia in the summer of 1979, raining some parts onto the ocean's surface. "This debris would burn up on entry and there would be no real impact," he adds. "There might be a big lightshow and there might be some pieces of the hardware that might survive the fall, but that would be about it. Also, it's more likely, much more likely to hit the Moon than the Earth."
The team still has to define absolutely, unequivocally that this object is the third stage of the Apollo rocket -- and they plan on seeing this project through to the very end. "There is work still to do," confirms Chesley. "We want to definitively link this observed object with the object that was observed in 1971 and with Apollo 12 in 1969. We got as much observable data as we could when we could see it [before it was ejected out into interplanetary space], and the research is ongoing. It's just not going very fast right now. We have other missions [but] when the decks get cleared, we're going to get after this again. And, in a perfect world, we'll be able to make that connection definitive with some more effort."
Once their work is complete, the team plans on documenting all the research in a journal.