Earlier this week asteroid Ryugu had a visitor. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu on October 3rd after it was successfully deployed from the Japanese Hayabusa2 space probe. The little hopping robot’s visit was brief however, and it stopped functioning on Oct. 4th.
In December of 2014, the Japanese Aerospace Exploration Agency (JAXA) launched the Hayabusa2 mission. As the second spacecraft to bear this name, Hayabusa2 was deployed by JAXA to conduct a sample-return mission with an asteroid. By studying samples of the near-Earth asteroid 162173 Ryugu, scientists hope to shed new light on the history of the early Solar System
The spacecraft arrived in orbit around Ryugu in July of 2018, where it will spend a total of a year and a half surveying the asteroid before returning to Earth. On September 23rd, the satellite deployed its onboard MINERVA-II rovers onto the surface of Ryugu. According to the latest updates from JAXA, both rovers are in good condition and have recently sent back photographs and a video of the asteroid’s surface.
In all this time, the question of ‘Oumuamua’s origin has remained unanswered. Beyond theorizing that it came from the direction of the Lyra Constellation, possibly from the Vega system, there have been no definitive answers. Luckily, an international team led by researchers from the Max Planck Institute for Astronomy (MPIA) have tracked ‘Oumuamua and narrowed down its point of origin to four possible star systems.
Within near-Earth space, there are over 18,000 asteroids whose orbit occasionally brings them close to Earth. Over the course of millions of years, some of these Near-Earth Objects (NEOs) – which range from a few meters to tens of kilometers in diameter – may even collide with Earth. It is for this reason that the ESA and other space agencies around the world are engaged in coordinated efforts to routinely monitor larger NEOs and track their orbits.
In addition, NASA and other space agencies have been developing counter-measures in case any of these objects stray too close to our planet in the future. One proposal is NASA’s Double Asteroid Redirection Test (DART), the world’s first spacecraft specifically designed to deflect incoming asteroids. This spacecraft recently moved into the final design and assembly phase and will launch to space in the next few years.
Within Earth’s orbit, there are an estimated eighteen-thousands Near-Earth Asteroids (NEAs), objects whose orbit periodically takes them close to Earth. Because these asteroids sometimes make close flybys to Earth – and have collided with Earth in the past – they are naturally seen as a potential hazard. For this reason, scientists are dedicated to tracking NEAs, as well as studying their origin and evolution.
Roughly 4.5 billion years ago, scientists theorize that Earth experienced a massive impact with a Mars-sized object (named Theia). In accordance with the Giant Impact Hypothesis, this collision placed a considerable amount of debris in orbit, which eventually coalesced to form the Moon. And while the Moon has remained Earth’s only natural satellite since then, astronomers believe that Earth occasionally shares its orbit with “mini-moons”.
These are essentially small and fast-moving asteroids that largely avoid detection, with only one having been observed to date. But according to a new study by an international team of scientists, the development of instruments like the Large Synoptic Survey Telescope (LSST) could allow for their detection and study. This, in turn, will present astronomers and asteroid miners with considerable opportunities.
The study which details their findings recently appeared in the Frontiers in Astronomy and Space Sciences under the title “Earth’s Minimoons: Opportunities for Science and Technology“. The study was led by Robert Jedicke, a researcher from the University of Hawaii at Manoa, and included members from the Southwest Research Institute (SwRI), the University of Washington, the Luleå University of Technology, the University of Helsinki, and the Universidad Rey Juan Carlos.
As a specialist in Solar System bodies, Jedicke has spent his career studying the orbit and size distributions of asteroid populations – including Main Belt and Near Earth Objects (NEOs), Centaurs, Trans-Neptunian Objects (TNOs), comets, and interstellar objects. For the sake of their study, Jedicke and his colleagues focused on objects known as temporarily-captured orbiters (TCO) – aka. mini-moons.
These are essentially small rocky bodies – thought to measure up to 1-2 meters (3.3 to 6.6 feet) in diameter – that are temporarily gravitationally bound to the Earth-Moon system. This population of objects also includes temporarily-captured flybys (TCFs), asteroids that fly by Earth and make at least one revolution of the planet before escaping orbit or entering our atmosphere.
As Dr. Jedicke explained in a recent Science Dailynews release, these characteristics is what makes mini-moons particularly hard to observe:
“Mini-moons are small, moving across the sky much faster than most asteroid surveys can detect. Only one minimoon has ever been discovered orbiting Earth, the relatively large object designated 2006 RH120, of a few meters in diameter.”
This object, which measured a few meters in diameter, was discovered in 2006 by the Catalina Sky Survey (CSS), a NASA-funded project supported by the Near Earth Object Observation Program (NEOO) that is dedicated to discovering and tracking Near-Earth Asteroids (NEAs). Despite improvements over the past decade in ground-based telescopes and detectors, no other TCOs have been detected since.
After reviewing the last ten years of mini-moon research, Jedicke and colleagues concluded that existing technology is only capable of detecting these small, fast moving objects by chance. This is likely to change, according to Jedicke and his colleagues, thanks to the advent of the Large Synoptic Survey Telescope (LSST), a wide-field telescope that is currently under construction in Chile.
Once complete, the LSST will spend the ten years investigating the mysteries of dark matter and dark energy, detecting transient events (e.g. novae, supernovae, gamma ray bursts, gravitational lensings, etc.), mapping the structure of the Milky Way, and mapping small objects in the Solar System. Using its advanced optics and data processing techniques, the LSST is expected to increase the number of cataloged NEAs and Kuiper Belt Objects (KBOs) by a factor of 10-100.
But as they indicate in their study, the LSST will also be able to verify the existence of TCOs and track their paths around our planet, which could result in exciting scientific and commercial opportunities. As Dr. Jedicke indicated:
“Mini-moons can provide interesting science and technology testbeds in near-Earth space. These asteroids are delivered towards Earth from the main asteroid belt between Mars and Jupiter via gravitational interactions with the Sun and planets in our solar system. The challenge lies in finding these small objects, despite their close proximity.”
When it is completed in a few years, it is hoped that the LSST will confirm the existence of mini-moons and help track their orbits around Earth. This will be possible thanks to the telescope’s primary mirror (which measures 8.4 meters (27 feet) across) and its 3200 megapixel camera – which has a tremendous field of view. As Jedicke explained, the telescope will be able to cover the entire night sky more than once a week and collect light from faint objects.
With the ability to detect and track these small, fast objects, low-cost missions may be possible to mini-Moons, which would be a boon for researchers seeking to learn more about asteroids in our Solar System. As Dr Mikael Granvik – a researcher from the Luleå University of Technology, the University of Helsinki, and a co-author on the paper – indicated:
“At present we don’t fully understand what asteroids are made of. Missions typically return only tiny amounts of material to Earth. Meteorites provide an indirect way of analyzing asteroids, but Earth’s atmosphere destroys weak materials when they pass through. Mini-moons are perfect targets for bringing back significant chunks of asteroid material, shielded by a spacecraft, which could then be studied in detail back on Earth.”
As Jedicke points out, the ability to conduct low-cost missions to objects that share Earth’s orbit will also be of interest to the burgeoning asteroid mining industry. Beyond that, they also offer the possibility of increasing humanity’s presence in space.
“Once we start finding mini-moons at a greater rate they will be perfect targets for satellite missions,” he said. “We can launch short and therefore cheaper missions, using them as testbeds for larger space missions and providing an opportunity for the fledgling asteroid mining industry to test their technology… I hope that humans will someday venture into the solar system to explore the planets, asteroids and comets — and I see mini-moons as the first stepping stones on that voyage.”
Since that time, multiple studies have been conducted to learn more about this interstellar visitor, and some missions have even been proposed to go and study it up close. However, the most recent study of ‘Oumuamua, conducted by a team of international scientists, has determined that based on the way it left our Solar System, ‘Oumuamua is likely to be a comet after all.
As noted, when it was first discovered – roughly a month after it made its closest approach to the Sun – scientists believed ‘Oumuamua was an interstellar comet. However, follow-up observations showed no evidence of gaseous emissions or a dusty environment around the body (i.e. a comet tail), thus leading to it being classified as a rocky interstellar asteroid.
This was followed by a team of international researchers conducting a study that showed how ‘Oumuamua was more icy that previously thought. Using the ESO’s Very Large Telescope in Chile and the William Herschel Telescope in La Palma, the team was able to obtain spectra from sunlight reflected off of ‘Oumuamua within 48 hours of the discovery. This revealed vital information about the composition of the object, and pointed towards it being icy rather than rocky.
The presence of an outer-layer of carbon rich material also explained why it did not experience outgassing as it neared the Sun. Following these initial observations, Marco Micheli and his team continued to conduct high-precision measurements of ‘Oumuamua and its position using ground-based facilities and the NASA/ESA Hubble Space Telescope.
By January, Hubble was able to snap some final images before the object became too faint to observe as it sped away from the Sun on its way to leaving the Solar System. To their surprise, they noted that the object was increasing its velocity deviating from the trajectory it would be following if only the gravity of the Sun and the planets were influencing its course.
In short, they discovered that ‘Oumuamua was not slowing down as expected, and as of June 1st, 2018, was traveling at a speed of roughly 114,000 km/h (70,800 mph). The most likely explanation, according to the team, is that ‘Oumuamua is venting material from its surface due to solar heating (aka. outgassing). The release of this material would give ‘Oumuamua the steady push it needed to achieve this velocity.
As Davide Farnocchia, a researcher from NASA’s Jet Propulsion Laboratory and a co-author on the paper, explained in a recent ESA press release:
“We tested many possible alternatives and the most plausible one is that ’Oumuamua must be a comet, and that gasses emanating from its surface were causing the tiny variations in its trajectory.”
Moreover, the release of gas pressure would also explain how ‘Oumuamua is veering off course since outgassing has been known to have the effect of perturbing the comet’s path. Naturally, there are still some mysteries that still need to be solved about this body. For one, the team still has not detected any dusty material or chemical signatures that typically characterize a comet.
As such, the team concluded that ‘Oumuamua must have been releasing only a very small amount of dust, or perhaps was releasing more pure gas without much dust. In either case, ‘Oumuamua is estimated to be a very small object, measuring about 400 meters (1312 ft) long. In the end, the hypothesized outgassing of ‘Oumuamua remains a mystery, much like its origin.
In fact, the team originally performed the Hubble observations on ‘Oumuamua in the hopes of determining its exact path, which they would then use to trace the object back to its parent star system. These new results mean this will be more challenging than originally thought. As Olivier Hainaut, a researcher from the European Southern Observatory and a co-author on the study, explained:
“It was extremely surprising that `Oumuamua first appeared as an asteroid, given that we expect interstellar comets should be far more abundant, so we have at least solved that particular puzzle. It is still a tiny and weird object, but our results certainly lean towards it being a comet and not an asteroid after all.”
Detlef Koschny, another co-author on the study, is responsible for Near-Earth Object activities under ESA’s Space Situational Awareness program. As he explained, the study of ‘Oumuamua has provided astronomers with the opportunity to improve asteroid detection methods, which could play a vital role in the study of Near-Earth Asteroids and determining if they post a risk.
“Interstellar visitors like these are scientifically fascinating, but extremely rare,” he said. “Near-Earth objects originating from within our Solar System are much more common and because these could pose an impact risk, we are working to improve our ability to scan the sky every night with telescopes such as our Optical Ground Station that contributed to this fascinating discovery.”
Since ‘Oumuamua’s arrival, scientists have determined that there may be thousands of interstellar asteroids currently in our Solar System, the largest of which would be tens of km in radius. Similarly, another study was conducted that revealed the presence of an interstellar asteroid (2015 BZ509) that – unlike ‘Oumuamua, which was an interloper to out system – was captured by Jupiter’s gravity and has since remained in a stable orbit.
This latest study is also timely given the fact that June 30th is global “Asteroid Day”, an annual event designed to raise awareness about asteroids and what can be done to protect Earth from a possible impact. In honor of this event, the ESA co-hosted a live webcast with the European Southern Observatory to discuss the latest science news and research on asteroids. To watch a replay of the webcast, go to the ESA’s Asteroid Day webpage.
The HubbleSpace Telescope is the oldest space telescope in operation, having spent the past twenty-eight years in orbit. Nevertheless, this mission is still hard at work revealing things about our Solar System, neighboring exoplanets, and some of the farthest reaches of the Universe. And every so often, it also captures an image that happens to turn up something interesting and unexpected.
Recently, while conducting a study of Abell 370, a galaxy cluster located approximately four billion light-years away in the constellation Cetus (the Sea Monster), Hubble managed to spot something in foreground. While observing this collection of several hundred galaxiess, the image was photobombed by 22 asteroids whose tails created streaks that looked like background astronomical phenomena.
The study was part of the Frontier Fields program, where Hubble has captured images of some of the earliest galaxies in the Universe (aka. “relic galaxies”) in order to determine how it evolved over time. The position of this asteroid field is near the ecliptic (the plane of our Solar System) where most asteroids reside, which is why Hubble astronomers saw so many crossings.
In the past, Hubble has recorded many instances of asteroid trails when conducting observations along a line-of-sight near the plane of our Solar System. In this case, the Near-Earth Asteroids (NEAs) – which orbit Earth at an average distance of about 260 million km (161.5 million mi) – were previously undetected due to their faintness. But thanks to the images taken by Hubble, scientists were able to identify them manually based on their motion.
Of the 22 asteroids, five were identified as unique objects. The image was assembled from several exposures taken in visible and infrared light, which was first released on November 6th, 2017. The image was prepared in honor of “Asteroid Day”, a global annual event that takes place every June 30th to raise awareness about asteroids and what can be done to protect Earth from a possible impact.
The day falls on the anniversary of the Tunguska event, which took place on June 30th, 1918, in eastern Russia and resulted in the flattening of 2,000 square km (770 square mi) of forest. While far less harmful than the Cretaceous–Paleogene (K–Pg) extinction event – which took place 66 million years ago and is believed to have killed the dinosaurs – Tunguska was the most harmful asteroid event in recorded history.
In many of the images snapped by Hubble, the asteroid tails appeared as white trails that look like curved streaks, an effect caused by parallax. In astronomy, parallax is an observational effect where the apparent position of an object appears to be different based on different lines of sight. Basically, as Hubble orbited around the Earth and took several images of the galaxy, the asteroids appeared to be moving relative to the background stars and galaxies.
The asteroids own motion along their orbits and other contributing factors also led to their streaked appearance. Whereas the white streaks were identified as asteroid tails, the blue streaks are distorted images of distant galaxies behind the cluster. This effect is known as gravitational lensing, where light from distant objects is warped and magnified by the presence of an intervening object.
In this case, the intervening object who’s gravitational force magnified the light of the background galaxies was Abell 370. These more distant galaxies are too distant for Hubble to see directly, hence why astronomers use the technique to study the most distant objects in the Universe. But whereas the blue streaks were expected, the white streaks caused by asteroids took scientists completely by surprise!
This year, the European Space Agency (ESA) is co-hosting a live webcast with the European Southern Observatory (ESO) with expert interviews, news on some the most recent asteroid research, and a discussion about what killed the dinosaurs. You can watch this event tomorrow starting at 13:00 CEST (11:00 UST/04:00 PST) by going to the ESA’s Asteroid Day web page.
Up for a challenge? Planetary action is certainly heating up this summer: Jupiter passed opposition last month, Saturn does so in June, and Mars reaches favorable viewing next month. And with dazzling Venus in the west and Mercury to joining it starting in late June, we’ll soon have all of the naked eye classical planets in the evening sky.
Now, I want to turn your attention towards a potential naked eye object, one you’ve probably never seen: asteroid 4 Vesta.
Vistas of Vesta
Vesta reaches opposition in 2018 on the night of June 19th. At 1.14 Astronomical Units (AU, 170.8 million kilometers) distant, this year’s opposition is slightly more favorable than any other since 1989. We won’t get another pass nearly as close until May 2036. Vesta orbits the Sun once every 3.6 years, ranging from a perihelion of 2.15 AU to an aphelion of 2.57 AU.
Although Vesta was the fourth asteroid discovered, it’s actually the brightest, and the only one visible with the naked eye—that is, if you have dark skies, and know exactly where to look for it. This summer, Vesta loiters in the star rich realm of the astronomical constellation Sagittarius, “in the weeds” for viewers up north, but high in the sky for southern viewers.
Early June finds Vesta about 5 degrees northwest of the +3.8 magnitude star Mu Sagittarii, threading between the deep sky objects Messier 24 and Messier 25. Vesta then loops westward through the constellation Ophiuchus the Serpent Bearer starting on July 1st, before heading back to Sagittarius on September 5th.
Vesta in 2018
Catching Vesta with the naked eye isn’t easy. You’ll need dark rural skies with a limiting magnitude down to about +5.5, and a good beforehand knowledge of the fixed stars in the region. Vesta also spends 2018 weaving around the star-dappled plane of the Milky Way galaxy, making it an especially challenging target.
Binoculars or a telescope can bring the challenge within reach of suburban and urban skies, making it a pleasure to trace the track of Vesta from night to night. Sketch the background star field and you just might tease out the presence of Vesta as it slowly moves about 30′ arcminutes per night (the diameter of a Full Moon) through June. Crank up the magnification a bit using a large (10 inches aperture or greater) light bucket telescope, and you just might see the faint hint of an oblong disk… 348 by 277 miles (560 by 446 kilometers) in size, Vesta’s apparent size is 0.7” arcseconds around opposition, 1/3 the size of Neptune at its best.
The 99% illuminated, waxing gibbous Moon will actually occult 4 Vesta for Hawaii, Central America and the Galapagos Islands just eight days after opposition on the night of June 27th.
Discovered on the night of March 29th, 1807 by prolific asteroid hunter Heinrich Olber, the Hubble Space Telescope gave us our first blurry images of 4 Vesta back in 2007. NASA’s Dawn spacecraft gave us our first good views of Vesta as a world starting in mid- 2011, orbiting the potato-shaped asteroid for just over a year before departing for 1 Ceres in late 2012.
Attack of the Vestoid(s)
And did you know: we actually have identified samples of Vesta to study, right here on Earth. Vesta sustained a massive impact about a billion years ago, raining debris through the inner solar system. Dawn chronicled the resulting Rheasilvia impact basin on Vesta’s south pole, and asteroids such as 1981 Midas match the spectral composition of Vesta and are collectively known as “Vestoids”.
On Earth, meteorites such as QUE 97053 found in Antarctica and the 1913 Moore County fall in North Carolina also match up in composition to Vesta, and make up a subgroup known as Howardite-Eucrite-Diogenite (HED) meteorites. Collectively, space rocks from this single impact on 4 Vesta contribute to an amazing 5% of all the meteorites recovered on Earth.
Fascinating thoughts to ponder, as we follow the brightest asteroid through the summer sky.