EROS ENCOUNTER 2019
(posted October 15, 2018)
(modified October 31, 2018)
|Within the next few months I have an opportunity to relive one of the most important, and pivotal, events of my career as an astronomer. In doing so as I begin to approach what will likely be the twilight of that career, I would like to share this "reliving" in the expectation that there are young budding astronomers all over the world who will share this event with me and help me in "passing the torch" to younger generations who will help in fulfilling the Earthrise vision and in building a better future for all of humanity.
That pivotal event in the early days of my career involves an asteroid that was discovered as long ago as August 1898 by Gustav Witt at the Berlin Observatory (and independently the same night by Auguste Charlois at the Nice Observatory in France). While every one of the 400+ known asteroids at that time orbited within the main "asteroid belt" between Mars and Jupiter, this new discovery surprised everyone by not only crossing within the orbit of Mars but actually coming quite close to Earth on occasion -- indeed, it had passed only 0.152 AU (14.2 million miles, or 22.8 million km) from Earth in January 1894, 4 1/2 years before its discovery. The newly discovered asteroid was soon named Eros, after the Greek god of love; it orbits the sun every 1.76 years (21 months) in a moderately elongated orbit (eccentricity 0.223) that brings it to 1.133 AU from the sun at perihelion and takes it out to 1.783 AU -- somewhat beyond the orbit of Mars -- at aphelion. Physical studies indicate it is quite elongated (21 miles by 7 miles by 7 miles, or 34 km by 11 km by 11 km) and rotates in 5.3 hours.
Eros made its next close approach to Earth in January 1931, when it passed 0.174 AU (16.2 million miles, or 26.1 million km) from our home planet. Among the various investigations that were conducted around that time were parallax studies which helped define the exact size of an Astronomical Unit (AU) that in turn helped put the distance scale of the solar system on a firm footing. These measurements set the standard for these determinations until radar- and spacecraft-based methods superseded them in the 1960s.
In January 1975 Eros passed 0.151 AU (14.1 million miles, or 22.6 million km) from Earth, the closest approach it has made to our home planet since its discovery. At that time I was 16 years old, and in my Junior year (11th Grade) in high school. I had acquired my first telescope (a 4.5-inch, or 11.4-cm, reflector) five years earlier and had been actively observing the night sky ever since, including several comets (my lifetime comet tally being 14 at the time). I observed Eros on several occasions during its encounter with Earth, and it was as bright as 7th magnitude and easily visible with binoculars.
But I did more than just "observe" Eros during that encounter with Earth. In what I now consider to be my "breakout" astronomical study, and with the aid and mentorship of a local amateur astronomer, Phil Simpson* (at that time a U.S. Air Force officer stationed at the nearby Holloman Air Force Base) who in turn helped me gain access to the 12.5-inch (32 cm) reflector owned by the local school system, I carried out a full-blown investigation of Eros as a Science Fair project. During the course of this project I carried out a series of continuous brightness measurements over two nights to determine Eros' rotation period, calculated its brightness parameters (including its geometric albedo) and its average orbital velocity as well as its velocities at perihelion and aphelion, and even took a stab at predicting the path of an occultation it would make of the star Kappa Geminorum.
|The display for my Science Fair project (which my father helped me construct) included the pedestal of a bird bath, into the top of which I inserted a large bolt. On top of this bolt I placed a log, spray-painted black, which I intended to represent both Eros' elongated shape and its relatively dark surface. The log could be spun around the bolt, which was designed to represent Eros' rotation.
To my rather delighted surprise, my project was warmly received by the various judges throughout the Science Fair program, and I won First Place in the Earth and Space Science Division at the Local, Regional, and State Science Fairs (as well as various other awards). From the perspective of my future career, an even more important event took place at the Regional Science Fair that was held at the campus of New Mexico State University in Las Cruces, where one of the judges was Dr. Herb Beebe, at that time the Head of the Astronomy Department at the University. After introducing himself to me, Dr. Beebe and I had a long and involved discussion at the Fair, and that initial meeting turned into a long-lasting friendship. That friendship played a non-trivial role in my decision over a decade later to enter graduate school at NMSU, where I would eventually earn my Ph.D. in Astronomy in 1992. Although Dr. Beebe formally retired during my time as a graduate student, he stayed on as Professor Emeritus, and served on my doctoral committee -- and I remember his commenting after my defense about the long road I had traveled since high school.
|Display for my Science Fair project on Eros, circa March-April 1975.|
|Eros would once again become an object of high scientific interest at the very end of the 20th Century and beginning of the 21st Century. In February 2000 the Near-Earth Asteroid Rendezvous (NEAR) spacecraft -- renamed NEAR Shoemaker in honor of the late planetary geologist Eugene "Gene" Shoemaker -- approached Eros and went into orbit around it, becoming the first spacecraft to orbit an asteroid. NEAR Shoemaker spent the next year extensively studying Eros and taking detailed photographs of its surface, which revealed numerous impact craters as well as a significant number of large boulders, most of which are believed to have resulted from one large impact event a long time ago. At the completion of its mission NEAR Shoemaker approached Eros and performed a soft landing upon its surface on February 12, 2001, in the process becoming the first spacecraft to land upon an asteroid.|
|Image of Eros obtained by the NEAR Shoemaker spacecraft on February 14, 2000. Readers can evaluate for themselves how closely the "true" Eros resembles -- or does not resemble -- the black log I used in my High School Science Fair project. Image courtesy NASA.|
|Around that same time, during the latter months of 2000 I was busily attempting to initiate an astrometric observation program, with help from a grant I had been awarded by the Foundation for the International Non-governmental Development of Space (FINDS) and with a telescope and CCD camera donated by Meade Instruments. In October I was formally assigned an Observatory Code (921) by the IAU's Minor Planet Center. Although Eros did not come close to the Earth that year -- the closest approaching being 0.76 AU in mid-July -- it nevertheless was observable, and I successfully obtained visual observations and CCD images on one night in late September, and the astrometric measurements I made were subsequently published in the November batch of the Minor Planet Circulars Supplement.|
|LEFT: Two CCD images I took of Eros on the evening of September 28, 2000, approximately 68 minutes apart. Eros is marked in the upper image, and its motion by the lower image is obvious. RIGHT: Excerpt from MPS 21769 dated November 11, 2000, with the astrometric measurements (highlighted) of Eros I obtained from the two images.
I continued the astrometric program for several more years, and among my accomplishments with it were confirmations of a couple of comet discoveries, and some measurements of Comet 81P/Wild 2 that were crucial in navigating the Stardust mission to its encounter with that object in early 2004. (One of the images I obtained of that comet when it was passing by the Crab Nebula M1 was featured on the homepage of the Stardust web site for a while.) The donated telescopes are still functional (although in need of some minor repairs) but the cameras are now outdated; meanwhile, my funding ran out (and FINDS no longer exists as an institution). At the same time, my focus turned more towards the outreach and bridge-building aspects of Earthrise, and with all of this combined I terminated the astrometric program some years ago. My life and career during the intervening years have been "interesting" in a number of ways, and I have recounted some of the happenings and the activities I have been involved in elsewhere on this web site.
Just like everything else in the solar system, meanwhile, Eros has continued its regular orbits around the sun, and in January 2012 it passed 0.179 AU (16.6 million miles, or 26.7 million km) from Earth. I observed it visually on a handful of occasions then as it reached close to 8th magnitude, but did not perform any detailed studies of it otherwise.
|Eros is now approaching Earth again, and on January 15, 2019, it will pass 0.209 AU (19.4 million miles, or 31.2 million km) from our home planet -- the fourth-closest approach it has made since its original discovery, and the third-closest approach in my lifetime. At this writing it is about 11th magnitude and is located in northeastern Perseus; it is slowly traveling northward, and when at opposition near the end of November it will be in Camelopardalis at a declination of +62 degrees. Eros then begins descending southward and crosses back into Perseus, and when nearest Earth (when there will be a first-quarter moon in the evening sky) it will be in the southeastern reaches of that constellation. It should be around 9th magnitude at that time, but will then fade slowly as it continues its southward trek (into Taurus and then on into the rich star fields of the wintertime Milky Way) and pulls away from Earth.|
|(433) Eros on October 10, 2018, as imaged by the Las Cumbres Observatory facility at McDonald Observatory in Texas.|
|While I expect to obtain more visual observations of Eros this time around, as in 2012 I don't really plan to engage in any detailed scientific investigations of it; and, truth be told, in light of NEAR Shoemaker there probably isn't all that much more knowledge we can gain of Eros from ground-based observations anyway. However . . . Eros holds a significant place in the history of our efforts to understand the solar system, and as I have detailed here it occupies a significant place in my own personal career history as well. I therefore encourage astronomy students, and educators and educational institutions, around the world to take advantage of this opportunity to examine this historically significant resident of our solar system. Perhaps there are students who might wish to recreate some of the measurements I made all those years ago . . . and, of course, we have equipment today that was not available or accessible back then. When nearest Earth, Eros will be easily detectable with even small backyard telescopes (and, at least from dark rural sites, even with binoculars), and it will be conveniently accessible in the evening sky. I stand ready to assist any students and educators who might wish to call on me for such assistance; this includes the taking of images with the Las Cumbres Observatory with which I am collaborating. (Note: ephemerides for Eros -- and any other asteroids and comets -- can be calculated using the ephemeris service at the Minor Planet Center's web site; for Eros enter "433" in the "objects" box.)
It's worth mentioning that it will be a long time before Eros comes anywhere near this close again; indeed, it doesn't even approach to within 0.35 AU of Earth until 2049. It doesn't come closer to Earth than the current approach until seven years after that, when in January 2056 Eros passes just 0.150 AU (13.9 million miles, or 22.4 million km) from Earth, marginally closer than it approached in 1975. I would be 97 years old at the time, and I remember pointing this out to some of my science-minded friends back when I was in high school; one of them joked that I could do another Science Fair project at that time . . . Well, we'll see about that . . . but, perhaps some of the students who might be observing Eros this time around will be part of an expedition to that object then, and perhaps will have made contributions toward building a better world that will be worthy of such an endeavor.
*(ADDED OCTOBER 31, 2018): I have just recently learned that Phil Simpson, who mentored me on my high school Science Fair project on Eros -- and who, in fact, initially suggested that studying Eros would be a worthwhile project for me to pursue in the first place -- passed away a little over a month ago. Phil and I had remained in occasional contact over the years, and I visited his home and observatory on a couple of occasions when he lived outside of Cloudcroft several years ago. My last contact with him came when he kindly sent me a copy of his book about the constellations. I am truly saddened to learn of his passing, and I always have been -- and will be -- grateful to him for taking that high school-age budding astronomer under his wing all those years ago, and in a very real sense getting me started on my eventual career.
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