Following is a NASA press release on mini-comets, based on the paper given this week by Lou Frank at the American Geophysical Union spring meeting, plus some commentary on Frank's hypothesis.
David Morrison, NASA AMES RESEARCH CENTER
POLAR SPACECRAFT IMAGES SUPPORT THEORY OF INTERPLANETARY SNOWBALLS SPRAYING EARTH'S UPPER ATMOSPHERE
Images from NASA's Polar spacecraft provide new evidence that Earth's upper atmosphere is being sprayed by a steady stream of water-bearing objects comparable to small comets.
Using Polar's Visible Imaging System (VIS), a research team led by Dr. Louis A. Frank of the University of Iowa in Iowa City has detected objects that streak toward Earth, disintegrate at high altitudes and deposit large clouds of water vapor in the upper atmosphere. Frank's research is being reported in a news briefing at 10 a.m. today at the spring meeting of the American Geophysical Union at the Convention Center in Baltimore, MD.
The incoming objects, which Frank estimates to be the size of a small house, pose no threat to people on Earth, nor to astronauts in orbit. "They break up and are destroyed at 600 to 15,000 miles above the Earth," Frank noted. "In fact, this relatively gentle 'cosmic rain' -- which possibly contains simple organic compounds -- may well have nurtured the development of life on our planet."
"This is an intriguing result that requires further scientific investigation," said Dr. George Withbroe, science director for the Sun-Earth Connection program in NASA's Office of Space Science. "We need to look closely at measurements from other sensors to find out if they see related signatures in the atmosphere, now that we have learned more about what to look for."
The Polar cameras have imaged trails of light in both ultraviolet and visible wavelengths as the objects disintegrate above the atmosphere. Using a filter that detects visible light emitted only by fragments of water molecules, Frank has shown that the objects consist primarily of water.
"The Polar results definitely demonstrate that there are objects entering the Earth's upper atmosphere that contain a lot of water," commented Dr. Thomas M. Donahue, a noted atmospheric physicist and professor at the University of Michigan in Ann Arbor.
"The images show that we have a large population of objects in the Earth's vicinity that have not been detected before," said Frank, who designed the VIS instrument. "We detect these objects at a rate that suggest Earth is being bombarded by five to 30 small comets per minute, or thousands per day." Comets are known to contain frozen water and are sometimes called "dirty snowballs".
Frank's new observations are consistent with a controversial theory he proposed in 1986 to explain the existence of dark spots, which he termed "atmospheric holes", in images of the sunlit atmosphere of the Earth. He first detected these holes while analyzing data from an ultraviolet imager flown on NASA's Dynamics Explorer 1 spacecraft. He theorized that the holes were caused by the disintegration of small icy comets in the upper atmosphere. The water vapor they produce momentarily absorbs the ultraviolet solar radiation scattered from oxygen atoms in the upper atmosphere, preventing it from reaching his camera and resulting in a dark spot on the image. These holes have diameters of 1 5 to 25 miles.
His theory of a new class of objects in the Solar System ignited a wide-ranging controversy. Many colleagues discounted the appearance of the holes as an instrumental problem. But the new images from Polar also include observations of atmospheric holes in much greater detail than before, suggesting that they are real. "These results certainly vindicate Lou Frank's earlier observations", said Donahue.
"These remarkable images cap a great first year for Polar," added Dr. Robert Hoffman, Project Scientist for Polar, which is operated and managed by NASA's Goddard Space Flight Center, Greenbelt, MD. "I am pleased that Polar's instruments were able to actually detect these objects streaking towards the Earth and disintegrating into clouds of water vapor. They give scientists a fascinating new and important phenomenon to take into account in theories of Solar System evolution."
Images of the comets and the atmospheric holes can be found on the World Wide Web at the following URL:
COMMENTS ON INTERPLANETARY SNOWBALLS
It should be remembered that Lou Frank has not detected mini-comets directly, and at issue should be his interpretation of the spacecraft data. This has been missed in most of the press reports I have seen, which assume that his mini-comet hypothesis of 1986 is now verified. But we must remember that the impact rate proposed by Lou Frank for 5-m comets is about a million times greater than that given by a power-law size distribution, which is well anchored by observations of objects just an order of magnitude higher than the sizes that Frank suggests are so abundant. Is it physically possible for the numbers of NEOs to increase by six orders of magnitude in the one order of magnitude size range from 50 m to 5 m diameter? I think we should all be skeptical. I look forward to seeing a refereed, published paper on these results and their interpretation. And we should all ask if these objects could have been missed by other detection techniques, including our eyeballs looking up at the night sky. After all, he is talking about roughly Hiroshima size flashes happening at a rate of 10 per minute, rather than the accepted rate of once every few months. How could these have been missed?
Following are some additional comments from Al Harris (JPL):
1. If they are there we should see them. We know within a factor of a few what the flux of ~5m sized objects is. We may arguably not know if they are ice or rock or metal, or their density, or their albedos, but within reasonable limits we certainly know the numbers to better than an order of magnitude, and Frank's numbers are a million or so too high. If there really were that many 5 m objects out there, even at albedo 0.05, you should be able to see several in an evening scanning the sky with binoculars: about one per 400 sq. deg. at magnitude 8.5, and moving at about the speed of a slow earth satellite.
2. Nothing breaks up at "600 to 15,000 miles above the Earth." Not even icy fluff balls, certainly not a 5 meter object which weighs 30 tons. Anything so weak as to come apart in that environment wouldn't stay intact even in heliocentric orbit.
3. The mass he proposes (~10/minute impacts of ~30 tons) adds up to a fair fraction of the Earth's mass (~10-20%) in the age of the solar system. That's about 1 cm of water a decade, which is measurable. The oceans aren't rising that fast, and certainly haven't for a geologically significant length of time.
Dear friends and students of NEOs:
Following are edited comments that I have received from a variety of colleagues concerning the Lou Frank mini-comet hypothesis, for those who want more details. Also, at the end, I include a story from the British tabloid press showing how this story can be distorted to serve other agendas. It is increasingly my impression that the British press is less accurate and less responsible than the American, at least in reporting science!
>From Yvonne Pendleton (NASA Ames):
The water level in the stratosphere is well accounted for and the influx from these "comets" would be greatly noticed. We fly the KAO and SOFIA there to enjoy the benefit of the dryness!
The IDP (interplanetary dust) count rate would be increased dramatically if these were comets in any true sense of the word, therefore, whatever they are they must be nearly pure water. Otherwise the release of the water would liberate the dust and the IDP count would be much higher.
I don't see how these things can be so fluffy that they disperse at 600 miles up, but stay intact until them. And what could their point of origin be?
The Moon would show the accumulation of a thin atmosphere over 4.5 billion years' of bombardment by these pure water snowballs, I beleive. There would also be Moon quakes generated by the kinetic energy of the objects, even if they are this fluffy stuff.
How does one get a gentle rain at our surface when the molecules dissociated up high -- and how did these molecules completely by-pass the stratosphere.
>From Don Teomans (JPL):
Frank is talking about objects the size of "small houses" or 10-20 m sized objects. At the rates he's talking about, the lunar surface should be COVERED with very fresh 150 m sized craters and the Apollo astronauts would have certainly noticed a flux of this magnitude. If I'm not mistaken, Apollo also left seismometers on the lunar surface that should have detected this flux. I don't know what Frank is seeing, but his suggested flux of mini-comet just doesn't hold water (sorry - couldn't resist).
>From Ted Bunch (NASA Ames):
With this flux of small objects, we should see a very high, small-impact erosion rate on the moon and probably Mars regardless of the low density of these objects. Objects 5-20 m in dia. with a D = 0.2 g/cc will still erode visible features in a short period of time. We have experimental evidence for that (Vertical gun impact erosion rates). To my knowledge, nothing like this is evident on the surface of moon or Mars or anywhere else. - ----------
>From Chris Chyba (University of Arizona):
If the flux of supposed comets was steady through the past 10 to 100 Myr, then siderophile abundances from ocean sediments would be 10^6 higher than they are (the measured quantities are in agreements with the known meteorite (mostly IDP) flux). One way around this, of course, is for Frank's objects to simply lack the usual cosmic abundances of siderophiles. These must be truly remarkable objects! They are nearly pure water, with densities of fresh snow, no siderophiles to speak of, but have a dark coating (must be on the outside only) to protect them from rapid sublimation (I am reaching back to Frank's models of the 1980s for this). They also can't couple their impact energy efficiently with the Moon, or Apollo seismometers would have detected them. Is all this possible? Yes it is, but the objects begin to have a very "contrived" feel to them.
>From Mark Boslaugh (Sandia Lab):
According to Frank (GRL, April, 1986, p.310): "The number density of these small comets in the vicinity of earth is ~10-20 comet/m3, including a factor of ~2 for gravitational focusing. If these comets are distributed with constant number density in the disk in the ecliptic plane, and centered on the sun, with thickness 1 A.U. and radius 1000.AU the total number of comets in theis volume is ~10E20. The corresponding mass is ~10E25 kg, somewhat larger than the earth's mass."
Frank also asserts that textbooks will have to be rewritten in scores of subject areas. Certainly conservation of momentum and energy does not apply to his comets, so one of these subjects is physics.
Please add impact physicists to the list of scientists who do not believe Frank's small comets hypothesis.
>From Mike A'Hearn (University of Maryland):
I am simply unconvinced that asteroidal searches even see the comets of the same size as the asteroids they detect. The coma inhibits most of the automatic detection schemes rather than helping. After lengthy discussions with Ted Bowell and Bruce Koehn during my last observing run in Flagstaff, they agreed that their planned detection scheme would not find comets. Bruce is now looking at various binning approaches to see if there is some simple way of detecting them. The only comets detected by Spacewatch have been ones that were seen visually on the screen by the observer sitting in the control room. They were not found by the software. I have never seen a description of the NEAT algorithm so I don't know how good it is on comets (actually if you have a good description of the algorithm I would be interested since at least NEAT did find a couple of comets!)
I do have serious problems with the mass flux implied by Lou Franks' interpretation and, as Jack Brandt has pointed out, we are proposing to search for fluxes of bodies that are orders of magnitude lower than what Lou Frank claimed from his DE results. I therefore don't really trust him either but his new data are clearly telling us something interesting and I would like to know what it is.
Reply to A'Hearn from Al Harris (JPL):
Your point that automated searches probably miss comets is well taken. However, as I pointed out, Lou Frank's flux estimate implies that you should see these things with a pair of binoculars in the evening sky at the rate of one every few minutes. In the case of someone staring up with binoculars, a coma can only help. So his hypothesis is wacko.
>From Al Harris to Dick Kerr on the detection issues:
Even if you allow an albedo of 0.005 (4-8 times darker than anything we have ever measured in space), the "comets" would be mag. 10 instead of 8.5, and still one per 400 sq. deg. of sky -- easily visible to anyone with a pair of binoculars and a few minutes to spare looking at the sky any evening. The "search ... done by the late Clayne Yeates" was horribly flawed, as much so as Frank's comet hypothesis itself. The problem was that they assumed that the "comets" were in zero eccentricity, zero inclination orbits around the sun, so that the Spacewatch telescope could track on them at exactly -0.5 deg/day from sidereal rate at opposition. What they saw in the field were trailed stars and lots of dots, the latter they interpreted as being Frank's comets. Anyone who has ever used a CCD knows you get lots of dots -- noisy pixels, cosmic ray hits, just random fluctuations of noise. An example of an almost identical experiment was Cochran et al's search with HST for small KB comets. They were smarter than Yeates and realized the problem of noise. In a careful analysis, they determine that almost half of what they scored as "detections" must be noise because they can get a half-score by co-adding for other rates of motion. People are still arguing if the other half of the claimed detections might also be noise, but that's another story. Anyway, in the Yeates experiment they must all be noise, because the underlying assumption of circular orbital motion is dynamical fiction -- it just can't be so. Just like the hypothesis of the mini-comets itself, it leads to such preposterous contradictions of what we know quite reliably to be correct, that a responsible scientist will desist and look elsewhere for an explanation.
>From Tom Gehrels (University of Arizona) on detection:
There is one other aspect though that we should investigate before carrying interpretations too far.
Lou put a few interesting pictures on his Web site. However, his statistics probably come from those splotches "observed" on the top of the Earth's atmosphere. I learned 10 years ago, in a similar situation, that when he wants to find something, he is not critical.
His statistics, his large numbers, are the issue, and that should be checked. Whereas right now the world may be in awe of those (few) trails seen in his pictures, the basis for his statistics should be gone over objectively.
>From A'Hearn on detection:
The automated detection schemes which I understand (Spacewatch and LONEOS but not NEAT) are constructed in such a way that they will not find large, fuzzy objects, even if they are brighter than an easily findable point source. Every active comet found by Spacewatch has been found not by software but by the observer at the console seeing it on the screen. There is therefore a bias against seeing active comets. I agree that inactive comets would be found since they would look just like asteroids. Ted Bowell and Bruce Koehn are now exploring alternative algorithms to figure out how they might search for comets with LONEOS because they agree that their algorithms would miss the active comets. The activity makes a comet more visible to a visual observer but not to currently used algorithms. Just think about the fact that comet Hale-Bopp was very bright, within two magnitudes of its discovery magnitude, for at least two years prior to its discovery according to the images on pre-discovery photographs. Think also that, despite the existence of the Shoemaker's Palomar survey and the Spacewatch survey in 1990-95 AND STILL the NEAT survey and the Spaceatch survey since then, 2/3 of the known comets coming inside Earth's orbit in both of those time periods have been discovered by amateurs when they were far, far brighter than the detection limits of the cited surveys. Part of this is, of course, the fact that the existing surveys have focused on the ecliptic where the asteroids are and most comets are not in the ecliptic. The point is that we are not looking for faint comets systematically. I will have to go back again to Rabinowitz's work and see how sensitive his conclusions are to assumed distributions with inclination.
I agree that Lou's numbers imply far too many of these objects even for me to believe and I worry about them being a misinterpretation. The case that Jack Brandt and several others of us have been making for a couple of years is to look for a population that we predict to be orders of magnitude smaller than Lou Frank's population but we really do think that there is a large, undiscovered population out there. On the other hand, I have looked at Lou's latest data and I am convinced that he is seeing something real - the question is what it is that he is seeing.
>From Paul Weissman (JPL):
All the previous criticisms about Frank's suggestion are still valid: they should have been detected in lunar seismic data from the Apollo sites; they should produce a substantial number of visible bolides; they should have been found by Spacewatch and NEAT; they should produce interplanetary UV from OH that was not seen by Voyager or Galileo, etc.
It is worth noting that in 1986 Frank was talking about 100 meter objects, whereas now he refers to 10 meter objects. So the effective masses of his objects have come down by a factor of 1,000. I presume that this is because of better observational data, but may also be due to having better absorption cross-sections for OH in the UV and other factors in his estimate of the sizes that are better known now than they were 11 years ago.
It is of course dangerous to extrapolate from only two points, but it could be that the estimated dimensions and masses of these objects will continue to decline with time and better modeling. Obviously, they have a long way to go to match what we currently understand is the flux of near-Earth objects, but at least the latest numbers are less inconsistent with reality than previously.
Frank continues to dig himself into a deeper and deeper hole with the bizarre physics he invokes to make the objects undetectable by other means. Eeventually that will rise up to smite him down in a very convincing way (to everyone but him, of course).
- ------------ - ------------
>From John Lewis (University of Arizona):
It's astonishing that Donahue, of all people, accepts this interpretation. He has steadfastly opposed the argument forwarded by Dave Grinspoon and myself (Icarus 74, 21-35, 1988) that cometary infall delivers water to Venus at an average rate roughly equal to the observed hydrogen escape rate. That rate is 10,000 times lower than the infall rate he now seems to favor via these putative microcomets! In other words, Venus, far from being in the final stages of drying out from the loss of a global ocean, would (if these enormous infall rates are correct) acually be increasing in water content at such a rate that it must have started out absolutely free of water only 30,000 years ago!
Note that the infall rate we favored was based on large comet and asteroid impacts, not on ANY form of microcomets.
And what about the cratering data on the Moon? Where are the 10^6 times as many small craters? According to Shoemaker, they don't exist.
Note that cometary ices bearing dust, organics, and salts should give whopping "flame tests" upon entry due to the Swann bands of C2 and the sodium D emission, among others. These are not stealth entry vehicles!
>From Lindley Johnson (USAF Space Command):
I saw this press release in our local paper the other day and my reaction certainly was "What has this guy been smoking?!?" I'm surprised to learn this theory is being seriously discussed. I'll check around, but I'm not aware that DoD sensors are detecting anything like this, and I would think we would if it were real.
>From Jeff Bell (University of Hawaii):
The new mini-comet affair has made be realize a scary fact: I no longer believe official NASA press releases. Neither do most of my friends. The process of reporting scientific work has become so distorted that people on the outside can no longer get a balanced view of what we really know about important space science issues.
[Bell then lists a number of past examples]
Case 5: Mini-comets. This hypothesis was endlessly discussed in the 1980s and firmly rejected by everybody but the author, who in fact exhibits all the characteristics of a crank. Yet here it is back again, endorsed by NASA as a major discovery.
All these cases of hype run wild may serve the short-range purpose of keeping valuable projects funded, but they have the long-term effect of eroding the credibility of NASA, and the space science community in general. If I don't trust official NASA press releases on topics like this, how can I honestly tell a Dick Hoagland fan to trust what they say about the Face On Mars?
THE SUNDAY TELEGRAPH, 1 June 1997
ICE CUBES FROM SPACE PROVE THE SCOFFERS WRONG
Many scientists are having to eat humble pie this weekend, following the revelation that the Earth is constantly pelted by cosmic snowballs the size of houses. And not before time either, as these same scientists have spent a decade disparaging Dr Louis Frank of Iowa University for his refusal to bow to orthodoxy and deny the evidence of his own eyes.
That evidence first emerged in 1982, when a student of Dr Frank's was analysing images of the Earth sent back by two Nasa satellites. To the student's frustration, many of the images were spoiled by tiny black dots. At first sight, they appeared to be faulty data, but careful study revealed that they behaved far too regularly to be dismissed as random flaws.
Instead, they appeared to be tiny comet-like objects that were striking the atmosphere at a rate of one every three seconds, each dumping tons of water on to the Earth.
For a few years, other researchers showed no more than polite interest in Frank's claims when they were mentioned at conferences. It was when he tried to get his research published in academic journals that Frank discovered the fate that awaits those who make radical claims in science.
The leading journal NATURE rejected his claims, saying that "a representative poll" had been taken of experts in the field and they had voted against publication. Frank's attempt to answer his critics with fresh evidence by using major telescopes were met with obstruction and foot-dragging, with astronomers insisting that the enterprise was a waste of time.
When Frank did succeed in getting access to a telescope, it revealed objects streaking across the atmosphere at 20,000mph - as he had predicted. It made no difference: the findings were still rejected for publication.
Now, after 10 years of obstruction and ridicule, it is Frank's turn to laugh. Cameras he designed aboard Nasa's Polar spacecraft have revealed the existence of the small comets beyond all doubt. Spectacular images taken by cameras show the comets streaking into the atmosphere before dumping their water. They arrive at the rate of about one every three seconds - just as Frank had claimed.
Frank himself has always been surprisingly sanguine about the controversy, apparently taking the view that the "truth will out" (sic). But there is no getting around the fact that many scientists have taken a woefully unscientific approach to the whole issue.
While extraordinary claims must demand extraordinary evidence, the reluctance of many to consider Frank's evidence was matched only by their keenness to block his attempts to gather more.
Frank's experience in this quintessentially Strange but True story are far from unique. The whole issue of bombardment by cosmic debris is one that has always been dogged by mule-like intransigence dressed up as academic rigour.
Until the early 19th century, anyone claiming to have seen stones falling out of the sky was regarded as having had a few beers too many; the French Academy of Sciences even declared such claims to be a scientific absurdity.
When hundreds of stones were reported to have smashed on to the French village of L'Aigle in 1803, the Academy dispatched a young astronomer to debunk the story. He returned with bad news: the reports were correct. Everyone now accepts the existence of meteorites but the confirmation came too late to save hundreds of specimens from being unceremoniously thrown out of museums as "superstitious artefacts".
The now widely-accepted theory that a hugh meteor struck the Earth 65 million years ago, pushing the dinosaurs into extinction, also came in for a least as much abuse as the idea of micro-comets when it was originally proposed.
When the late Nobel Prize-winning physicist Luis Alvarez and his team first published their evidence for the giant impact in 1980, one authority described it as "a nutty theory of pseudoscientists posing as paleontologists". Today it is the nutters who argue against it.
There is one aspect of the Earth bombardment issue that remains a source of incredulity among many scientists: the idea that humanity is under serious threat from meteor impacts. The sceptics are still demanding hard evidence for this threat. We can only hope that the "hard evidence" doesn't come in form of a billion-tonne meteor any time soon.
Two major sites about Comet Hale-Bopp are being maintained at the Jet Propulsion Laboratory. Charles S. Morris and Ron Baalke have many comet images as well as explanations of what is going on.
Karen Meech of
the Institute for Astronomy of the University of Hawaii and the
Hawaii Institute for Geophysics also have interesting comet sites.
The Henry J. Buhl, Jr., Planetarium in Pittsburgh has an observing guide.
A cool site with information on comets is part of the Why Files, a product of the National Institute for Science Education. Cross references include Chiron, Hale-Bopp, and other comet cross-references.
A particularly spectacular color image with Comet Hyakutake B2 (C/1996 B2) near the sun, which is giving off a huge Coronal Mass Ejection, has been released.
THE COMET Late at night, I looked up at the deep and mystic sky and thought of the comet Hyakutake and gazed with a wonder-filled eye There it sat, like a white ink blot bigger than the rest dim, fuzzy, light, unclear but certainly the best Every night I saw it It looked much much more bright waving sapphire wisp of a tail as it sank into the night No one I know will see it again for about twenty thousand years we'll wait the heavens shall remain regular and the stars will still shine out late Where has it been, these centuries? I wonder what it's seen it tells, yet, a silent tale through its sparkle and its gleam It has glimpsed into worlds an has seen many stars it could have dodged 'round the moon and played hopscotch on Mars I wish it could speak of its journeys Or its exciting ports of call It can shimmer in the darkness, but that's 'bout all.
Nancy Lohmiller 5th grade, Cottage Street School, Sharon, MA
NASA has selected the Stardust mission in its series of Discovery missions. It will be launched in 1999 and will fly past comet Wild-2 in January 2004. While up close, it will photograph the comet's nucleus and also trap dust particles in an aerogel. The spacecraft will then return near earth, and a return capsule with the dust samples will parachute to Earth in January 2006, landing in a dry lake bed in Utah.
In Fig. 17-39, the two lower views of Comet P/Shoemaker-Levy 9 are interchanged. The fuzzier image at lower right is from July 1993, before the repair mission, and the clearer image at lower left is from January 1994, after the repair mission. STScI sent out the image assembled in this backwards order.
2060 Chiron, now suspected to be a comet, occulted a star in 1994. The results, obtained by James Elliot of M.I.T., using similar methods to that he used to discover the rings of Uranus, and colleagues, indicate that there are opaque parts of Chiron's atmosphere. Chiron seems to be within 148 and 208 km in diameter, which makes it about 40 times larger in diameter than typical comets. Chiron may be one of the Kuiper Belt objects. Chiron will reach perihelion in February 1996 in its 51-year orbit.
...please see the summary article by S. Alan Stern in Nature for 5 January 1995, pp. 23-24, and article by J. L. Elliot et al. in the same issue of Nature, pp. 46-49.
Clark Chapman has an interesting article on "making sense of Comet Shoemaker-Levy 9's rendezvous with Jupiter" in the 21 January 1995 New Scientist, pp. 30-35. Among the items discussed is why the Kuiper Airborne Observatory saw water in a spectrum only before the temperatures of the impact plumes cooled. Perhaps the oxygen from the water was converted into carbon monoxide, which had also been detected. It is not yet known whether the comet or Jupiter was the source of the water. Another question raised is why all the impacts were so similar in extent, given the differing sizes of the entering fragments. Chapman suggests that the resulting differences for the different fragments manifested themselves deep down, where we couldn't see them, after causing similar effects in the atmosphere. "It is as if we tried to determine, just from measuring how much water squirts from a hose, whether its source is a cistern or the whole city water supply." Finally, some of the stratospheric comtaminants came from the comet while others, like the molecular sulfur, were so plentiful that they could not have been brought by these fragments and thus must have come from Jupiter itself. Sulfur had not been detected directly on Jupiter before these events.
A naked-eye comet, C/1996 B2, was widely visible in March. It was discovered on January 30 by a Japanese amateur astronomer, Yuji Hyakutake, the second comet he had discovered within five weeks. (The "B" in B2 means the second half of January; the "2" means that it was the second comet discovered in that half-month.)
Comet Hyakutake B2 (the B2 distinguishes it from Hyakutake's other comet, which is also visible in the sky, though much fainter) came within only 9.5 million kilometers of Earth on March 25th, moving across the sky by the diameter of the Moon in only 40 minutes. From dark sites, over 20 degrees of tail was visible.
The bright moon then brightened the sky so much that the tail was no longer visible, but the comet and its tail should again be visible in late April.
The Solar and Heliospheric Observatory (SoHO), which can hide the solar photosphere so as to see the space near the sun in the sky, observed C/1996 B2 (Hyakutake) when it was near its perihelion.
Comet Hale-Bopp is still expected to be several times brighter in the spring of 1997 than Comet Hyakutake was this year.