Artist's impression of a Near-Earth Asteroid passing by Earth. Credit: ESA
Of the more than 600,000 known asteroids in our Solar System, almost 10 000 are known as Near-Earth Objects (NEOs). These are asteroids or comets whose orbits bring them close to Earth’s, and which could potentially collide with us at some point in the future. As such, monitoring these objects is a vital part of NASA’s ongoing efforts in space. One such mission is NASA’s Near-Earth Object Wide-field Survey Explorer (NEOWISE), which has been active since December 2013.
And now, after two years of study, the information gathered by the mission is being released to the public. This included, most recently, NEOWISE’s second year of survey data, which accounted for 72 previously unknown objects that orbit near to our planet. Of these, eight were classified as potentially hazardous asteroids (PHAs), based on their size and how closely their orbits approach Earth.
What if Earth had multiple moons? Our world has one large natural satellite, just over a quarter the diameter, 1/50th the volume, and less than 1/80th the mass of our fair world. In fact, the Earth-Moon system has sometimes been referred to as a “binary planet,” and our Moon stands as the largest natural satellite of any planet — that is, if you subscribe to bouncing Pluto and Charon out of “the club” — in contrast to its primary of any moon in our solar system.
But what if we had two or more moons? And are there any tiny “moonlet” candidates lurking out there, awaiting discovery and perhaps exploration?
While historical searches for tiny secondary moons of the Earth — and even “moons of our Moon” — have turned up naught, the Earth does indeed capture asteroids as temporary moons and eject them back into solar orbit from time to time.
Now, a recent paper out of the University of Hawaii written in partnership with the SETI Institute and the Department of Physics at the University of Helsinki has looked at the possible prospects for the population of captured Near-Earth asteroids, and the feasibility of detecting these with existing and future systems about to come online.
The hunt for spurious moons of the Earth has a fascinating and largely untold history. Arthur Upgren’s outstanding book Many Skies devotes an entire chapter to the possible ramifications of an Earth with multiple moons… sure, more moons would be a bane for astrophotographers, but hey, eclipses and transits of the Sun would be more common, a definite plus.
In 1846, astronomer Frederic Petit announced the discovery of a tiny Earth-orbiting moon from Toulouse observatory. “Petit’s Moon” was said to orbit the Earth once every 2 hours and 44 minutes and reach an apogee of 3,570 kilometres and a perigee of just 11.4 (!) kilometres, placing it well inside the Earth’s atmosphere on closest approach.
The announcement (in German) of the discovery of Waltemath’s Moon. “Ein zweiter Mond der Erde” translates into “a second Earth moon.” Credit: Wikimedia Commons image in the public domain.
A slightly more believable claim came from astronomer Georg Waltemath in 1898 for a moon 700 kilometres in size — he claimed it was, of course, a very dark body and not very easily visible — orbiting the Earth at about 2.5 times the distance of the Moon. Waltemath even made an announcement of his discovery, and claimed to have found a third moon of the Earth for good measure.
And a much more dubious claim came from the astrologer Walter Gornold in 1918 of a secondary moon, dubbed Lilith. Apparently, then (as now) astrologers never actually bothered to look at the skies…
Turns out, our large Moon makes a pretty good goaltender, ejecting —and sometimes taking a beating from — any tiny second moon hopeful. Of course, you can’t blame those astronomers of yore entirely. Though none of these spurious moons survived the test of observational verification, these discoveries often stemmed from early efforts to accurately predict the precise motion of the Moon. Astronomers therefore felt they were on the right track, looking for an unseen perturbing body.
Fast forward to the 21st century. Quasi-moons of the Earth, such as 3753 Cruithne, have horseshoe-shaped orbits and seem to approach and recede from our planet as both orbit the Sun. Similar quasi-moons of Venus have also been discovered.
And even returning space junk can masquerade as a moon of Earth, as was the case of J002E3 and 2010 QW1, which turned out to be boosters from Apollo 12 and the Chinese Chang’e-2 missions, respectively.
What modern researchers are looking for are termed Temporarily Captured Orbiters, or TCOs. The study notes that perhaps an average of a few dozen asteroids up to 1 to 2 metres in size are in a “steady state” population that may be orbiting the Earth at any given time on an enter, orbit, and eject sort of conveyor belt. Estimates suggest that a large 5 to 10 metre asteroid is captured every decade so, and a 100 metre or larger TCO is temporarily captured by the Earth every 100,000 years. The study also estimates that about 1% occasionally hit the Earth. And though it wasn’t a TCO, the ability to detect an Earthbound asteroid before impact was demonstrated in 2008 with the discovery of 2008 TC3, less than 24 hours prior to striking in the Sudanese desert.
“There are currently no projects that are solely looking for minimoons at this time,” lead researcher Bryce Bolin of the University of Hawaii told Universe Today. “There are several surveys, such as PanSTARRS, the Catalina Sky Survey and the Palomar Transit Factory that are currently in operation that have the capability of discovering minimoons.”
The convoluted orbit of 2006 RH120 around the Earth-Moon system, to date the only confirmed TCO. Credit: Wikimedia Commons/Ohms law.
We’re getting better at this hazardous asteroid detection business, that’s for sure. The researchers modeled paths and orbits for TCOs in the study, and also noted that collections may “clump” at the anti-sunward L2 opposition point, and the L1 sunward point, with smaller distributions located at the east and west quadrature points located 90 degrees on either side of the Earth. The L2 point in particular might make a good place to start the search.
Ironically, systems such as LINEAR and PanSTARRS may have already captured a TCO in their data and disregarded them in their quest for traditional Near Earth Objects.
“Surveys such as PanSTARRS/LINEAR utilize a filtration process to remove artifacts and false positives in the data as it gets processed through the data pipeline,” Researcher Bryce Bolin told Universe Today. “A common method is to apply a rate of motion cut… this is effective in eliminating many artifacts (which) tend to have a rate of motion as measured by the pipeline which is very high.”
Such systems aren’t always looking for fast movers near Earth orbit that can produce a trail or streak which may reassemble space junk or become lost in the gaps over multiple detection devices. And speaking of which, researchers note that Arecibo and the U.S. Air Force’s Space Surveillance System may be recruited in this effort as well. To date, one definite TCO, named 2006 RH120 has been documented orbiting and departing from the vicinity of the Earth, and such worldlets might make enticing targets for future manned missions due to their relatively low Delta-V for arrival and departure.
An artist’s concept of a possible future asteroid mission near Earth. Credit: NASA.
PanSTARRS-2 saw first light last year in 2013, and is slated to go online for full science operations by the end of 2014. Eventually, the PanSTARRS system will employ four telescopes, and may find a bevy of TCOs. The researchers estimate in the study that a telescope such as Subaru stands a 90% chance of nabbing a TCO after only five nights of dedicated sweeps of the sky.
Finally, the study also notes that evidence miniature moonlets orbiting Earth may lurk in the all sky data gathered by automated cameras and amateur observers during meteor showers. Of course, we’re talking tiny, dust-to-pebble sized evidence, but there’s no lower limit as to what constitutes a moon…
And so, although moons such a “Lilith” and “Petit’s Moon” belong to the annuals of astronomical history, temporary “minimoons” of Earth are modern realities. And as events such as Chelyabinsk remind us, it’s always worthwhile to hunt for hazardous NEOs (and TCOs) that may be headed our way. Hey, to paraphrase science fiction author Larry Niven: unlike the dinosaurs, we have a space program!
Read more about the fascinating history of moons that never were and more in the classic book The Haunted Observatory.
PHA asteroid 2014 KM4 on approach to Jupiter in late 2021. Credit: the Solar System Dynamics JPL Small-Body Database Browser.
A recent space rock discovery has sent a minor buzz through the community that tracks such objects. And as usual, it has also begun to attract the dubious attention of those less than honorable sites — we won’t dignify them with links — that like to trumpet gloom and doom, and we thought we’d set the record straight, or at very least, head the Woo off at the pass as quickly as possible.
The asteroid in question is 2014 KM4. Discovered earlier this month, this 192 metre space rock safely passed by the Earth-Moon system at 0.17 A.U.s distant on April 21st. No real biggie, as asteroids pass lots closer all the time. For example, we just had a 6-metre asteroid named 2014 KC45 pass about 48,000 miles (about 80,000 kilometres) from the Earth yesterday morning. That’s about twice the distance of the orbit of geosynchronous satellites and 20% the distance to the Moon.
Sure, it’s a dangerous universe out there… you only have to stand in the Barringer Meteor Crater in Arizona outside of Flagstaff or watch the videos of a meteor exploding over Chelyabinsk last year the day after Valentine’s Day to know that. But what makes 2014 KM4 interesting is its orbit and its potential to approach Jupiter in about seven years.
Or not. One dilemma with orbital mechanics is that the precision of a known orbital path relies on the number of observations made and that position gets more and more uncertain as we project an object’s position ahead in space and time. 2014 KM4 is on a 5.08 year orbit inclined 5.2 degrees to the ecliptic plane that brings it juuusst inside the Earth’s orbit — hence the Apollo designation — and out to an aphelion point very near Jupiter at 5.2 A.U.s from the Sun. But that’s only based on 14 observations made over a span of 5 days. The current nominal trajectory sees 2014 KM4 pass about 0.1 A.U. or 15.5 million kilometres from Jupiter on January 16th 2022. That’s inside the orbit of Jupiter’s outermost moons, but comfortably outside of the orbit of the Galilean moons. The current chance of 2014 KM4 actually impacting Jupiter sits at around 1% and the general trend for these kinds of measurements is for the probability to go down as better observations are made. This is just what happened last year when comet 2013 A1 Siding Spring was discovered to pass very close to Mars later this year on October 19th.
We caught up with JPL astronomer Amy Mainzer, Principal Investigator on the NEOWISE project currently hunting for Near Earth Asteroids for her thoughts on the subject.
“The uncertainty in this object’s orbit is huge since it only has a 5 day observational arc,” Mainzer told Universe Today. “A quick check of the JPL NEO orbit page shows that the uncertainty in its semi-major axis is a whopping 0.47 astronomical units! That’s a huge uncertainty.”
“At this point, any possibility of impact with Jupiter is highly uncertain and probably not likely to happen. But it does point out why it’s so important to extend observational arcs out so that we can extend the arc far enough out so that future observers can nab an object when it makes its next appearance.”
Jupiter takes a beating from Comet Shoemaker-Levy 9. Credit: NASA/Hubble Space Telescope team.
IF (that less than 1% “IF”) 2014 KM4 were to hit Jupiter, it would represent the most distant projection ahead in time of such an event. About two decades ago, humanity had a front row seat to the impact of comet Shoemaker-Levy 9 into Jupiter in July 1994. At an estimated 192 metres in size, 2014 KM4 is about the size of the “D” fragment that hit Jupiter on July 17th 1994. 2014 KM4 has an absolute magnitude (for asteroids, this is how bright they’d appear at 1 A.U. distant) of +21.3 and is currently well placed for follow up observations in the constellation Virgo.
And astronomer Nick Howes mentioned to Universe Today that the Faulkes Telescope North may soon be used to make further observations of 2014 KM4. In the meantime, you can enjoy the animation of their observations of another Near-Earth Asteroid, 2014 KP4.
An animation of the motion of PHA asteroid 2014 KP4. Credit: Remanzacco Observatory.
And yes, the 2022 pass of 2014 KM4 near Jupiter will modify the orbit of the asteroid… but not in our direction. Jupiter is a great “goal tender” in this regard, protecting the inner solar system from incoming hazards.
2014 KM4 is well worth keeping an eye on, but will most likely vanish from interest until it returns to our neck of the solar system in 2065. And no, a killer asteroid won’t hit the Earth in 2045, as a CNN iReport (since removed) stated earlier this week… on “March 35th” no less. Pro-tip for all you conspiracy types out there that think “Big NASA” is secretly hiding the next “big one” from the public: when concocting the apocalypse, please refer to a calendar for a fictional date that at least actually exists!
This model of the half-kilometer near-Earth asteroid Golevka, color-coded for gravitational slope. Credit: NASA
[/caption]
It’s one of the scariest scenarios that could face Earth. Can you imagine an asteroid impact? Even if it were a small event, it could have some far-reaching implications for life of all types here on terra firma. Knowing where and what we might be facing has been of constant concern, but one of the biggest problems is that there isn’t enough “eyes on the skies” to go around. There’s always a possibility that a flying space rock could slip through the proverbial cracks and devastate our planet. But, no worries… We’ve got a student to put to the test!
While most asteroids belong to the Jupiter-orbit class and pose absolutely no danger to Earth, there are exceptions to every rule. Known as Near Earth Objects (NEO), these orbiting stones also share our orbit – and our paths could cross. However, the juxtaposition is that we need to uncover as many of these stragglers as we can, document and track them for the most accurate information possible. Why? We need precise orbital information… A “somewhere in the neighborhood” just won’t do. By knowing exactly what’s out there, we stand a true chance of being able to deflect a problem before it arises. Right now a program headed by Mark Trueblood with Robert Crawford (Rincon Ranch Observatory) and Larry Lebofsky (Planetary Science Institute) is being executed at the National Optical Astronomy Observatory to help catalog NEOs – and it’s being assisted by a Beloit College student, Morgan Rehnberg, who developed a computer program called PhAst (for Photometry and Astrometry) that’s available over the Internet.
Because asteroids have a speedy window of observing opportunity, there can be no delays in reporting and tracking data. Time is of the element. While most astronomy targets are of long term imaging, asteroids require multiple digital images which are viewed via the “blink” method – similar to an old nickelodeon movie. At the same time, the coordinates for the NEO must be perfected and then computed. Right ascension and declination must be absolutely spot on. While there are computer programs currently able to do just that, none of them did exactly what’s required to stake the life of planet Earth on. Even though a better software program was required, there simply wasn’t enough time for the group to write it – but Trueblood saw it as the perfect opportunity for a summer student.
Many of us are familiar with the Research Experience for Undergraduates (REU) program, supported by the National Science Foundation and part of the National Optical Astronomy Observatory (NOAO). Not only has the REU made some fine imaging contributions, but they’ve learned what having a career in astronomy is really like and gone on to become professionals themselves. Enter Morgan Rehnberg, who just happened to have the right computer skills needed to tweak the current image viewer program (ATV, written in the code IDL) . Now you have a recipe for checking out as many images as needed in any order, and perform the astrometric (positional) as well as photometric (brightness) analyses.
While Morgan initially put his new software to use on existing image data, the first test happened this October during an observing session using the 2.1m telescope at Kitt Peak National Observatory. It was definitely a yellow alert when the group happened across a Potentially Hazardous Asteroid (PHA) designated as NEO2008 QT3. This wasn’t just a close rock… this was a rock that was going to pass within 50,000 km of Earth! Thanks to Morgan’s software upgrades, the team was able to correctly compute the brightness and distance of the PHA with 50% of the error margin gone. The resulting positional information was then submitted to the Minor Planet Center and accepted.
It’s a good thing they did it… PhAst!
Original Story Source: NOAO News. The computer program PhAST is available at http://www.noao.edu/news/2011/pr1107.php. In addition to the multi-object support, it contains the ability to calibrate images, perform astrometry (using the existing open source packages SExtractor, SCAMP, and missFITS), and construct the reports for the Minor Planet Center.
