New System Discovered with Five Planets

A new study announced the discovery of a new system hosting five transiting planets (image credit: jhmart1/deviantart).
A new study announced the discovery of a system hosting five transiting planets (image credit: jhmart1/deviantart).

NASA’s planet-discovering Kepler mission suffered a major mechanical failure in May 2013, but thanks to innovative techniques subsequently implemented by astronomers the satellite continues to uncover worlds beyond our Solar System (i.e., exoplanets).  Indeed, Andrew Vanderburg (CfA) and colleagues just published results highlighting a new system found to host five transiting planets, which include: two sub-Neptune sized planets, a Neptune sized planet, a sub-Saturn sized planet, and a Jupiter sized planet.

Continue reading “New System Discovered with Five Planets”

Radio waves absent from the reputed megastructure-encompassed Kepler star?

Astronomers at the SETI institute (search for extraterrestrial intelligence) have reported their findings after monitoring the reputed megastructure-encompassed star KIC 8462852.  No significant radio signals were detected in observations carried out from the Allen Telescope Array between October 15-30th (nearly 12 hours each day).  However, there are caveats, namely that the sensitivity and frequency range were limited, and gaps existed in the coverage (e.g., between 6-7 Ghz).

Lead author Gerald Harp and the SETI team discussed the various ideas proposed to explain the anomalous Kepler brightness measurements of KIC 8462852, “The unusual star KIC 8462852 studied by the Kepler space telescope appears to have a large quantity of matter orbiting quickly about it. In transit, this material can obscure more than 20% of the light from that star. However, the dimming does not exhibit the periodicity expected of an accompanying exoplanet.”  The team went on to add that, “Although natural explanations should be favored; e.g., a constellation of comets disrupted by a passing star (Boyajian et al. 2015), or gravitational darkening of an oblate star (Galasyn 2015), it is interesting to speculate that the occluding matter might signal the presence of massive astroengineering projects constructed in the vicinity of KIC 8462582 (Wright, Cartier et al. 2015).”

One such megastructure was discussed in a famous paper by Freeman Dyson (1960), and subsequently designated a ‘Dyson Sphere‘.  In order to accommodate an advanced civilisation’s increasing energy demands, Dyson remarked that, “pressures will ultimately drive an intelligent species to adopt some such efficient exploitation of its available resources. One should expect that, within a few thousand years of its entering the stage of industrial development, any intelligent species should be found occupying an artificial biosphere which completely surrounds its parent star.”  Dyson further proposed that a search be potentially conducted for artificial radio emissions stemming from the vicinity of a target star.



An episode of Star Trek TNG featured a memorable discussion regarding a ‘Dyson Sphere‘.

The SETI team summarized Dyson’s idea by noting that Solar panels could serve to capture starlight as a source of sustainable energy, and likewise highlighted that other, “large-scale structures might be built to serve as possible habitats (e.g., “ring worlds”), or as long-lived beacons to signal the existence of such civilizations to technologically advanced life in other star systems by occluding starlight in a manner not characteristic of natural orbiting bodies (Arnold 2013).”  Indeed, bright variable stars such as the famed Cepheid stars have been cited as potential beacons.



The Universe Today’s Fraser Cain discusses a ‘Dyson Sphere‘.

If a Dyson Sphere encompassed the Kepler catalogued star, the SETI team were seeking in part to identify spacecraft that may service a large structure and could be revealed by a powerful wide bandwidth signal.  The team concluded that their radio observations did not reveal any significant signal stemming from the star (e.g., Fig 1 below).  Yet as noted above, the sensitivity was limited to above 100 Jy and the frequency range was restricted to 1-10 Ghz, and gaps existed in that coverage.

Fig 1 from Harp et al. 2015 (http://arxiv.org/abs/1511.01606) indicating the lack of signal detected for the Kepler star (black symbols).
Fig 1 from Harp et al. (2015) conveys the lack of radio waves emerging from the star KIC 8462852 (black symbols), however there were sensitivity and coverage limitations (see text).  The signal emerging from the quasar 3c84 is shown via blue symbols.

What is causing the odd brightness variations seen in the Kepler star KIC 8462852?   Were those anomalous variations a result of an unknown spurious artefact from the telescope itself, a swath of comets temporarily blocking the star’s light, or perhaps something more extravagant.  The latter should not be hailed as the de facto source simply because an explanation is not readily available.  However, the intellectual exercise of contemplating the technology advanced civilisations could construct to address certain needs (e.g., energy) is certainly a worthy venture.

More Evidence that the Milky Way has Four Spiral Arms

Astronomers have been arguing over just how many spiral arms our Galaxy exhibits. Is the Milky Way a four or two-armed spiral galaxy? Astronomers had often assumed the Milky Way was potentially a four-armed spiral galaxy, but comparatively recent observations from NASA’s Spitzer telescope implied the Galaxy had two spiral arms.  In 2013, astronomers mapped star forming regions and argued they had found the two missing arms, bringing the total number of arms back to four.

The case for a four-armed Milky Way may have just gotten stronger.

A team of Brazilian astronomers used star clusters embedded in their natal clouds to trace the Galaxy’s structure. “Our results favour a four-armed spiral Galaxy, which includes the Sagittarius-Carina, Perseus, and Outer arms.”, remarked the group from the Universidade Federal do Rio Grande do Sul.

Image credit: Urquhart JS et al / Robert Hurt, the Spitzer Science Center / Robert Benjamin.
Spiral map of the Galaxy by Urquhart et al. 2013 (image credit: Urquhart et al. 2013, R. Hurt, the Spitzer Science Center, R. Benjamin).

“Despite efforts aimed at improving our understanding of the Galaxy’s structure, questions remain. There is no consensus regarding the number and shape of the Galaxy’s spiral arms.”, noted lead author D. Camargo.  He added that the Sun’s location within the obscured disc of the Galaxy was a principal factor hindering our understanding of the Milky Way’s broader structure.  In other words, we do not have a bird’s eye view of our Galaxy.

The team remarked that young embedded clusters are excellent tracers of the Galaxy’s structure, “The present results indicate that the Galaxy’s embedded clusters are predominantly located in the spiral arms.”  They noted that star formation may occur after the collapse and fragmentation of giant molecular clouds found within spiral arms, and consequently the young embedded star clusters that subsequently emerge are excellent probes of Galactic structure as they have not displaced far from their birthplace.

A projected face-on view of the distribution of embedded star clusters studied by Camargo et al. 2015. The objects appear to lie on the Sagittarius-Carina spiral arm, Perseus arm, and potentially an extension of the Outer arm (image credit: Camargo et al. 2015).

The team used data from NASA’s WISE infrared telescope to identify young clusters still embedded in their natal clouds, which are often encompassed by significant dust.  Infrared stellar light is less obscured by dust than visible light, giving the astronomers an unprecedented view.  Indeed, the group discovered 7 new embedded clusters, several of which (designated Camargo 441-444) may belong to a larger aggregate that resides in the Perseus arm.   They suggested that a giant molecular cloud was compressed by the spiral arm which may have triggered star formation in several clumps, and numerous star clusters with similar ages emerged (an alternative or concurrent scenario is sequential formation).

Astronomer A. Mainzer discusses NASA’s WISE telescope (Wide-Field Infrared Survey Explorer), which was used by Camargo et al. 2015 to identify embedded star clusters.

The team also used near-infrared data from the 2MASS survey to determine distances for the star clusters, once the objects were identified in the WISE images.  A primary goal of their work was to establish accurate fundamental cluster parameters, which would bolster any resulting conclusions concerning the Galaxy’s overall structure.   An innovative algorithm was therefore adopted to minimize contamination by foreground and background stars along the sight-line, which may otherwise appear as cluster members and degrade the reliability of any distant estimates.

“The embedded clusters in the present sample are distributed along the Sagittarius-Carina, Perseus, and Outer arms.”, concluded the team. They likewise noted that the search for new embedded clusters throughout the entire Galaxy must continue unabated, since such targets may foster our understanding of the Galaxy’s structure.

The discoveries are described in a new study by D. Camargo, C. Bonatto, and E. Bica that is entitled “Tracing the Galactic spiral structure with embedded clusters”. The research has been accepted for publication, and will appear in a forthcoming issue of the Monthly Notices of the Royal Astronomical Society (MNRAS).  A preprint of the work is available on arXiv.

‘Lopsided’ Supernova Could Be Responsible for Rogue Hypervelocity Stars

Hypervelocity stars have been observed traversing the Galaxy at extreme velocities (700 km/s), but the mechanisms that give rise to such phenomena are still debated.  Astronomer Thomas M. Tauris argues that lopsided supernova explosions can eject lower-mass Solar stars from the Galaxy at speeds up to 1280 km/s.   “[This mechanism] can account for the majority (if not all) of the detected G/K-dwarf hypervelocity candidates,” he said.

Several mechanisms have been proposed as the source for hypervelocity stars, and the hypotheses can vary as a function of stellar type.  A simplified summary of the hypothesis Tauris favors begins with a higher-mass star in a tight binary system, which finally undergoes a core-collapse supernova explosion.  The close proximity of the stars in the system partly ensures that the orbital velocities are exceedingly large.  The binary system is disrupted by the supernova explosion, which is lopsided (asymmetric) and imparts a significant kick to the emerging neutron star.  The remnants of supernovae with massive progenitors are neutron stars or potentially a more exotic object (i.e., black hole).

Conversely, Tauris noted that the aforementioned binary origin cannot easily explain the observed velocities of all higher-mass hypervelocity stars, namely the B-stars, which are often linked to an ejection mechanism from a binary interaction with the supermassive black hole at the Milky Way’s center.  Others have proposed that interactions between multiple stars near the centers of star clusters can give rise to certain hypervelocity candidates.

Certain astronomers argue that hypervelocity stars can stem from interactions in dense star clusters (image credit: Hubble)
Some astronomers argue that certain hypervelocity stars can stem from interactions in dense star clusters (image credit: NASA, ESA, and E. Sabbi (ESA/STScI))

There are several potential compact objects (neutron stars) which feature extreme velocities, such as B2011+38, B2224+65, IGR J11014-6103, and B1508+55, with the latter possibly exhibiting a velocity of 1100 km/s.  However, Tauris ends by noting that, “a firm identification of a hypervelocity star being ejected from a binary via a supernova is still missing, although a candidate exists (HD 271791) that’s being debated.”

Tauris is affiliated with the Argelander-Institut für Astronomie and Max-Planck-Institut für Radioastronomie. His findings will be published in the forthcoming March issue of the Monthly Notices of the Royal Astronomical Society.

The interested reader can find a preprint of Tauris’ study on arXiv.  Surveys of hypervelocity stars were published by Brown et al. 2014 and Palladino et al. 2014.

Searching for Alien Worlds and Gravitational Lenses from the Arctic

The quest for optimal sites to carry out astronomical observations has taken scientists to the frigid Arctic.  Eric Steinbring, who led a team of National Research Council Canada experts, noted that a high Arctic site can, “offer excellent image quality that is maintained during many clear, calm, dark periods that can last 100 hours or more.”  The new article by Steinbring and colleagues conveys recent progress made to obtain precise observations from a 600 m high ridge near the Eureka research base on Ellesmere Island, which is located in northern Canada.

The new telescope that Steinbring and his colleagues tested was located at the Polar Environment Atmospheric Research Laboratory (PEARL).  The observatory can be accessed in winter by 4 x 4 trucks via a 15 km long road from a base facility at sea-level. That base camp is operated by Environment Canada and serviced by an airstrip and resupply ship in summer.  Recently, wide-field cameras developed at the University of Toronto were deployed near Eureka to monitor thousands of stars, with the objective of expanding the exoplanet database.

Earlier work by Steinbring and colleagues indicated that data obtained from PEARL imply that clear weather prevails 68% of the time. After significant testing, the team concluded that the site “can allow reliable, uninterrupted temporal coverage during successive dark periods, in roughly 100 hour blocks with clear skies and good seeing.”

The Polar Environment Atmospheric Research Laboratory (PEARL) is located on Ellesmere Island (image credit: Left,  , right, Tobias Kerzenmacher).
The Polar Environment Atmospheric Research Laboratory (PEARL) is located on Ellesmere Island (image credit: left, wikimedia commons, right, Tobias Kerzenmacher).

However, the optimal conditions can be interrupted by brief but potentially intense storms. In the article the team added that, “the primary issue is wind rather than the cold temperatures.” The PEARL facility is equipped with an important weather probe that conveys on-site conditions at 10 minute intervals, thanks to the Canadian Network for the Detection of Atmospheric Change (CANDAC).

There are numerous challenges that arise when observing from the Arctic, but scientists like Steinbring have worked to overcome them, potentially enabling new studies of gravitational lenses and other pertinent phenomena. Indeed, astronomical observations are likewise being obtained from Antarctica. For example, there is the Antarctic Search for Transiting Exoplanets (ASTEP) 40 cm telescope at Dome C, and three 50 cm Antarctic Survey Telescopes (AST3) at Dome A, Antarctica. Steinbring remarked that floorspace is potentially available for up to 5 more telescopes at PEARL, if the compact design they studied was adopted.

E. Steinbring and his colleagues B. Leckie and R. Murowinski are associated with the National Research Council Canada, Herzberg Astronomy and Astrophysics in Victoria, Canada. An electronic preprint of their article is available on arXiv, and the findings were presented recently at the Adapting to the Atmosphere Conference in Durham, UK.

 

A Splash of Color Across the Supermoon

A software engineer from Florida recently captured an image of the day-old supermoon in September that clearly conveys color variations across its surface.  Such variations are often imperceptible, but the brightness and color differences were digitally enhanced to make them easier to discern.    The color variations are indicative of compositional differences across the Lunar surface (e.g., iron content and impact ejecta).

A supermoon is a full Moon that is observed during the satellite’s closest approach to Earth.  The Moon’s orbit is described by a marginally elongated ellipse rather than a circle, and hence the Moon’s distance from Earth is not constant. The Moon will achieve its largest apparent diameter in the Sky during that closest approach, which in part gives rise to the supermoon designation.

Noel Carboni, who imaged the supermoon a day after the full phase, told Universe Today that he, “created the image using 17 frames shot with a Canon EOS-40D, which was mounted to a 10-inch Meade telescope.”  He added that, “each exposure was 1/40th of a second, and a workstation was used to stitch the image which is more than 17,000 pixels square.”

Carboni noted that, “Ever since the 1980s, I have harbored a growing interest in digital imaging. It is exciting that nowadays affordable and high quality image capture equipment are available to consumers, and that formidable digital image processing tools are available to just plain folks!”

His astrophotography may be well known to readers of Universe Today, as his work has been featured on NASA’s Astronomy Picture of the Day (APOD) and elsewhere.  A gallery of Carboni’s astrophotography can be viewed at his webpage.

Readers desiring to learn more about the Moon and its surface can join the Moon Zoo Citizen Science Project, and glance at images from NASA’s Lunar Reconnaissance Orbiter.   The Moon Zoo project aims to inspect millions of images captured by that instrument, which will invariably help scientists advance our understanding of the Moon.

Too WISE to be Fooled by Dust: Over 300 New Star Clusters Discovered

Brazilian astronomers have discovered some 300+ star clusters that were largely overlooked owing to sizable obscuration by dust.  The astronomers, from the Universidade Federal do Rio Grande do Sul, used data obtained by NASA’s WISE (Wide-Field Infrared Survey Explorer) space telescope to detect the clusters.

“WISE is a powerful tool to probe … young clusters throughout the Galaxy”, remarked the group.  The clusters discovered were previously overlooked because the constituent stars are deeply embedded in their parent molecular cloud, and are encompassed by dust.   Stars and star clusters can emerge from such environments.

The group added that, “The present catalog of new clusters will certainly become a major source for future studies of star cluster formation.”   Indeed, WISE is well-suited to identify new stars and their host clusters because infrared radiation is less sensitive to dust obscuration.  The infrared part of the electromagnetic spectrum is sampled by WISE.

An optical (DSS) and infrared (WISE) image of the same field.  A cluster of young stars is not apparent in the optical (left) image owing to obscuration by dust.  However, a young star cluster is apparent in the right image because the dust reradiates the absorbed radiation in the infrared regime.  The new study highlights the discovery of numerous  star clusters discovered using infrared (WISE) data (image credit: DSS/NASA and assembly by D. Majaess).
An optical (DSS) and infrared (WISE) image of the same field. A cluster of young stars is not apparent in the optical (left) image owing to obscuration by dust.  However, a young star cluster is readily apparent in the right image because dust obscuration is significantly less at infrared wavelengths. A new study by a team of astronomers highlights the discovery of numerous star clusters using WISE data (image credit: DSS/NASA/IPAC and assembly by D. Majaess).

Historically, new star clusters were often identified while inspecting photographic plates imaged at (or near) visible wavelengths (i.e., the same wavelengths sampled by the eye).  Young embedded clusters were consequently under-sampled since the amount of obscuration by dust is wavelength dependent.  As indicated in the figure above, the infrared observations penetrate the dust by comparison to optical observations.

The latest generation of infrared survey telescopes (e.g., Spitzer and WISE) are thus excellent instruments for detecting clusters embedded in their parent cloud, or hidden from detection because of dust lying along the sight-line.  The team notes that, “The Galaxy appears to contain 100000 open clusters, but only some 2000 have established astrophysical parameters.”  It is hoped that continued investigations using WISE and Spitzer will help astronomers minimize that gap.

The discoveries are described in a new study by D. Camargo, E. Bica, and C. Bonatto that is entitled “New Glactic embedded cluster and candidates from a WISE survey“.   The study has been accepted for publication, and will appear in a forthcoming issue of the journal New Astronomy.  For more information on Galactic star clusters see the Dias et al. catalog, the WEBDA catalog, or the Star Clusters Young & Old Newsletter.  Thanks to K. MacLeod for the title suggestion.

The WISE (Wide-field Infrared Survey Explorer) space telescope was used to discover numerous new star clusters (image credit: NASA)(.
The WISE (Wide-field Infrared Survey Explorer) space telescope was used to discover numerous star clusters (image credit: NASA).

 

Young Boy’s Discovery Confirmed as a Peculiar Supernova Explosion

New observations confirm that young Nathan Gray’s discovery is indeed a supernova explosion, albeit a rather peculiar one.  Nathan Gray, age 10, discovered a new cosmic source on October 30th that emerged in the constellation of Draco, and it was subsequently classified as a supernova candidate.  Evidence available at the time was sufficiently convincing that Nathan was promptly heralded as the youngest individual to discover a supernova.

The discovery garnered world-wide attention, however, confirmation via a spectrum from a large telescope was necessary to unambiguously identify the target as a supernova.  In addition, that observation would enable astronomers to determine the supernova class and identify the progenitor of the exploding star.  In other words, was the star initially comparable in mass to the Sun and a member of a binary system, or was the original star significantly more massive and a neutron star is potentially all that remains?

The new observations were acquired by Lina Tomasella and Leonardo Tartaglia of the Padova-Asiago Supernova Group, and imply that the supernova stems from a star significantly more massive than the Sun.   Andrea Pastorello, a member of that group, noted that the target’s spectrum displays the presence of hydrogen (specifically H-alpha emission), which rules out the scenario of a lower-mass progenitor in a binary system (those are classified as type Ia).

Features present in the observations led the astronomers to issue a preliminary supernova classification of type II-pec (peculiar).  The blue spectral continuum is typical of a type IIn supernova, but the expansion velocity inferred from the hydrogen line (3100 km/s) is an order of magnitude larger than expected, which motivated the team to issue the aforementioned classification.  Pastorello further noted that the target is somewhat similar to SN 1998s, and in general type II supernovae exhibit heterogeneous observational properties.

Observations confirming that Nathan Gray's discovery is a supernova were obtained from the Asiago 1.82-m Copernico Telescope (image credit: L.C. / Istituto Nazionale di Astrofisica).
Observations confirming that young Nathan Gray’s cosmic discovery is a supernova were obtained from the Asiago 1.82-m Copernico Telescope (image credit: L.C. / Istituto Nazionale di Astrofisica).

Nathan had been scanning astronomical images sent by David J. Lane (Saint Mary’s University) for months, and identified some potential sources that proved to be false detections or previous discoveries.  However, the Padova-Asiago Supernova Group has now confirmed that isn’t the case this time.  Indeed, the discovery means that Nathan officially unseats his sister Kathryn as the youngest person to discover a supernova, yet she is elated for her bother (see Nancy Atkinson’s article regarding Kathryn’s discovery).

Nathan, his sister, and parents Paul and Susan, formed a supernova search team in partnership with Lane.  The original discovery images were obtained from the Abbey Ridge Observatory, which is stationed in Lane’s backyard.

Those desiring additional information on supernovae will find the videos below pertinent.


10-Year-Old Boy Discovers a 600 Million Year-Old Supernova

Young Canadian Nathan Gray, age 10, has discovered a supernova candidate in the field of the galaxy designated PGC 61330, which lies in the constellation of Draco (the dragon).

Nathan made the discovery while scanning astronomical images taken by Dave Lane, who runs the Abbey Ridge Observatory (ARO) which is stationed in Nova Scotia.  Incidentally, Nathan may unseat his older sister, Kathryn Aurora Gray, as the youngest supernova discoverer by a mere 33 days.

Nothing is visible at the location of the supernova candidate in prior images of the field taken over the past two years, or Digitized Palomar Sky Survey images.

Kathryn Aurora Gray garnered worldwide fame when she discovered a supernova in the galaxy designated UGC 3378 (see the Universe Today article by Nancy Atkinson). The discovery eventually earned her an audience with astronauts such as Neil Armstrong (shown below).

Kathryn Aurora Gray discovery of a supernova earned her the chance to meet Neil Armstrong, Bill Anders (Apollo 8), Victor Gorbakto, and Jim Lovell (Apollo 8 & 13).
Kathryn Aurora Gray’s discovery of a supernova earned her the chance to meet Neil Armstrong, Bill Anders (Apollo 8), Victor Gorbakto, and Jim Lovell (Apollo 8 & 13) (image credit: P. Gray/RASC).

Caroline Moore held the record prior to Kathryn as the youngest person to discover a supernova (Caroline was 14 at the time). Caroline subsequently had the honor of meeting President Obama at the White House (see the video below).

Supernova are immense explosions linked to the evolutionary end-state of certain stars. The explosions are so energetic that they can be observed in distant galaxies. Indeed, Nathan’s supernova could be some 600 million light years distant.  Gazing into space affords humanity the opportunity to peer back in time. Despite the (finite) speed of light being a remarkable 300000 km/s, the light-rays must travel over “astronomical” distances.

There are several different classes of supernovae. For example, Type II supernovae are associated with larger mass stars. The Sun will not terminate as a supernova, but may potentially evolve into a standard (or not) planetary nebula (see the Universe Today post “Astronomers Hint that our Sun won’t Terminate as the Typical Planetary Nebula”).

Nathan’s discovery has been posted on the International Astronomical Union’s site, and its presence confirmed by US and Italian-based observers. Its provisional name is: PSN J18032459+7013306, and to get an official supernova designation a large telescope needs to confirm the unique supernova light signature (via a spectrum).  Is the target a bona fide supernova?

“Given no motion, large distance from the galactic plane (ie. not likely a nova), and several optical confirmations, as well as its very close angular proximity to a faint galaxy, it is a supernova at any reasonable certainty,” said Lane, an astronomer in the Dept. of Astronomy & Physics at Saint Mary’s University, as well as the director of the Burke-Gaffney and Abbey Ridge astronomical observatories. “A significant fraction of
the supernova discoveries these days are not observed spectrographically due to the sheer number of them vs. telescope time.”

Nathan Gray is the son of Paul and Susan Gray.

*2013 10 31.9053 – update from the IAU: SN to be confirmed in PGC 61330 detected with 3 x 3 min images (exp 9 min). Astrometry: RA 18 03 24.12 Dec +70 13 26.4 (ref stars UCAC2) Photometry: 17.00CR +/-0.02 (USNO A2R Ref stars 163R, 170R, 172R, 173R). Measure on unfiltered image. Observer and measurer: Xavier Bros, ANYSLLUM OBSERVATORY, Ager, Spain. T-350mm f4.6. Link to image and further information: http://www.anysllum.com/PSN_PGC61330.jpg

Astronomers Stress the Need for Characterizing the Population of Nearby Potential Earth-Impactors

The meteor explosion over Russia in February 2013 raised concerns that even small asteroid impactors may wreak some havoc given our heavily populated cities.  A new study by NASA scientists aims to improve our understanding of such asteroids that are lurking in Earth’s vicinity.  The team, led by Amy Mainzer, noted that only a mere fraction of asteroids comparable in size to the object that exploded over Russia have been discovered, and their physical properties are poorly characterized.

The team derived fundamental properties for over a hundred near-Earth objects, and determined that many are smaller than 100 meters.  Indeed, the team notes that, “In general … [asteroids] smaller than 100-m are only detected when they are quite close … and the smallest … were detected when they were only 2-3 lunar distances away from Earth.”  

Essentially, a large fraction of these bodies may go undetected until they strike Earth, analogous to the case of the asteroid that exploded over Russia in February.

The team’s results rely partly on observations from the Wide-field Infrared Survey Explorer (WISE), which is a space-based telescope that mapped the entire sky in the mid-infrared. Observations taken in the infrared, in concert with those taken in the optical, can be used to infer the fundamental properties of asteroids (e.g., their diameter and chemical composition).

On a somewhat positive note, Mainzer remarks that 90% of near-Earth asteroids larger than 1-km are known, and those potential impactors are most worrisome as they may cause widespread fatalities.  The dinosaurs suffered a mass-extinction owing, at least in large part, to a 10-km impactor that struck Earth 65 million years ago.   However, Mainzer notes that the survey completeness drops to 25% for nearby 100-m asteroids, and it is likely to be less than 1% for 20-m asteroids like that which exploded over Russia (Chelyabinsk).  The Tunguska event (see the image below) is likewise speculated to have been on the order of that latter size.

In 1908 the Tunguska impactor toppled millions of trees in a rather remote part of Siberia.  The new study by Mainzer and coauthors aimed to better characterize the population of Tunguska-sized asteroids lurking in the vicinity of the Earth.
In 1908 the Tunguska meteor explosion toppled millions of trees in a rather remote part of Siberia. A new study by Mainzer et al. 2013 characterized 100+ objects lurking in the vicinity of the Earth that are on the order of the Tunguska impactor.

The team highlights that approximately 10,000 near-Earth objects have been discovered to date, 900 of which are 1-km or larger, and 3500 objects appear to be 100-m or smaller.  “Because their small sizes usually make them undetectable until they are very nearby the Earth, it is often difficult for the current suite of asteroid surveys and follow-up telescopes to track them for very long.

Consequently, the fraction of the total population at small sizes that has been discovered to date remains very low,” noted Mainzer.

In closing, Mainzer emphasizes that, “It is, however, clear that much work remains to be done to discover and characterize the population of very small NEOs [near-Earth objects].”


The Mainzer et al. 2013 findings have been accepted for publication in the Astrophysical Journal (ApJ), and a preprint is available on arXiv.  Coauthors on the study are J. Bauer, T. Grav, J. Masiero, R. M. Cutri, E. L. Wright, C. R. Nugent, R. Stevenson, E. Clyne, G. Cukrov, and F. Masci.