This image taken by the Mars Reconnaissance Orbiter's HiRise camera shows the bright landing platform left behind by NASA's Mars Exploration Rover Opportunity when it landed in 2004. Opportunity landed on the surface of Mars and then bounced and tumbled into the Eagle Crater. The image was taken on April 8, 2017. Image: NASA/JPL-Caltech/Univ. of Arizona
NASA’s eagle-eyed Mars Reconnaissance Orbiter (MRO) has captured orbital images of Opportunity’s Hole-In-One landing site, smack dab in the middle of Eagle Crater on the surface of Mars.
Opportunity arrived at Mars on January 25th, 2005. It’s landing was slowed by parachute, and cushioned by airbags. Once it hit the surface, it bounced its way into “Eagle Crater“, a feature a mere 22 meters across. Not a bad shot!
This is the first color image that the High Resolution Imaging Science Experiment (HiRise) has captured of Opportunity’s landing site. It shows the remarkable landing site inside the crater, where the landing pad was left behind after Opportunity rolled off of it and got going. It also shows the rover’s parachute and backshell.
It’s amazing that, given the relatively smooth surface in Opportunity’s landing area, the rover came to rest inside a small crater. When Opportunity “woke up” at its landing site, its first images were of the inside of Eagle Crater. This was the first look we ever got at the sedimentary rocks on Mars, taken by the rover’s navigation camera.
Opportunity’s navigation camera took this picture, one of the rover’s first, of the inside of Eagle Crater. Exposed Martian rocks are visible. NASA/JPL
After leaving Eagle Crater, Opportunity took a look back and captured a panoramic image. Plainly visible is the rover’s landing pad, the exposed sedimentary rock, and the rover’s tracks in the Martian soil.
This panorama image, called “Lion King” was assembled from 558 images totalling over 75 megabytes. The rock outcrop, the landing pad, and the rover’s tracks are all clearly visible. Image: NASA/JPL/Cornell
MRO arrived at Mars a couple years later, and by that time Opportunity had already left its landing site and made its way south to the much larger Victoria Crater.
When the Mars Reconnaissance Orbiter arrived at Mars, 2 years after Opportunity touched down there, Opportunity had left Eagle Crater and travelled the 6 km to Victoria Crater. By NASA/JPL/University of Arizona – http://photojournal.jpl.nasa.gov/catalog/PIA08813, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4211043
Opportunity is still chugging along, doing valuable work. And so is the MRO and its HiRise instrument. At this point, Opportunity has to be considered one of the most successful scientific undertakings ever.
Opportunity took this panorama shot of "Rocheport Ridge" as it left Cape Tribulation. Rocheport is on the southern end of Cape Tribulation. Image:NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.
You’d have to be an intrepid explorer to investigate something named ‘Cape Tribulation’. Opportunity, NASA’s long-lived rover on Mars’ surface, has been just that. But Opportunity is now leaving Cape Tribulation behind, after being in that area since late 2014, or for about 30 months.
Cape Tribulation is the name given to a segment of crater rim at Endeavour Crater, where Opportunity has been for over 5 1/2 years. During that time, Opportunity reached some important milestones. While there, it surpassed 26 miles in distance travelled, the length of a marathon race. It also reached its highest elevation yet, and in ‘Marathon Valley’, it investigated clay outcrops seen from orbit. Opportunity also had some struggles there, when its flash memory stopped working, meaning all data had to be transmitted every day, or lost.
Sol 3906, January 19, 2015. Summit panorama from Cape Tribulation from the Opportunity Mars Rover. Credit: NASA/Arizona State University.
Before reaching Cape Tribulation 30 months ago, Opportunity investigated other parts of Endeavour Crater called “Cape York,” “Solander Point” and “Murray Ridge.”
Some of the named features at Endeavour Crater. Image: NASA/JPL-Caltech/MSSS
The rover’s next destination is Perseverance Valley, where it will investigate how it was carved out billions of years ago: by water, by wind, or perhaps flowing material lubricated by water. Before leaving Cape Tribulation, Opportunity captured the panoramic image of Rochefort Ridge, a section of the Endeavour Crater rim marked by grooves on its side.”The degree of erosion at Rocheport is fascinating,” said Opportunity Deputy Principal Investigator Ray Arvidson, of Washington University in St. Louis. “Grooves run perpendicular to the crest line. They may have been carved by water or ice or wind. We want to see as many features like this on the way to Perseverance Valley as we can, for comparison with what we find there.”
Endeavour crater is about 22km in diameter, and Perseverance Valley is about 2 football fields long. The goal at Endeavour is to investigate its segmented rim, where the oldest rocks ever investigated on Mars are exposed. Since the beginning of April, Opportunity has travelled about 98 meters, to a point where Cape Tribulation meets the plain around the crater.
“From the Cape Tribulation departure point, we’ll make a beeline to the head of Perseverance Valley…” – Opportunity Deputy Principal Investigator Ray Arvidson
“From the Cape Tribulation departure point, we’ll make a beeline to the head of Perseverance Valley, then turn left and drive down the full length of the valley, if we can,” Arvidson said. “It’s what you would do if you were an astronaut arriving at a feature like this: Start at the top, looking at the source material, then proceed down the valley, looking at deposits along the way and at the bottom.”
It’s the nature of those deposits that can give vital clues to how Perseverance Valley was formed. Arvidson said, “If it was a debris flow, initiated by a little water, with lots of rocks moving downhill, it should be a jumbled mess. If it was a river cutting a channel, we may see gravel bars, crossbedding, and what’s called a ‘fining upward’ pattern of sediments, with coarsest rocks at the bottom.”
Opportunity, and its sister rover Spirit, arrived at Mars in 2004, with a planned mission length of 90 days. Opportunity has surpassed that by over 12 years, and continues to perform extremely well in the Martian environment.
According to a new study, EDLS hardware that has been jettisoned on Mars could create problems for future missions to the same landing sites. Credit: NASA
One of the most common features of space exploration has been the use of disposable components to get missions to where they are going. Whether we are talking about multistage rockets (which fall away as soon as they are spent) or the hardware used to achieve Entry, Descent and Landing (EDL) onto a planet, the idea has been the same. Once the delivery mechanism is used up, it is cast away.
However, in so doing, we could be creating a hazardous situation for future missions. Such is the conclusion reached by a new study from the Finnish Meteorological Institute in Helsinki, Finland. With regard to the use of Entry, Descent and Landing (EDL) systems, the study’s author – Dr. Mark Paton – concludes that jettisoned hardware from missions to Mars could create a terrible mess near future landing sites.
Dr. Mark Paton is a planetary research scientist who specializes in the interaction between the Martian atmosphere and its surface. As such, he is well-versed in the subject of EDL systems that are designed to land missions on Solar System bodies that have atmospheres. This is certainly a going concern for Mars, where landers and rovers have relied on various means to get to the surface safely.
Consider the Curiosity rover, which used a separate EDL system – known as the Sky Crane – to land on Mars in 2012. As the first EDL system of its kind, the Sky Crane was a essentially a rocket-powered backpack mounted on top of the rover. This system kicked in after Curiosity separated from its Descent module (which was slowed by a parachute) and used rockets to slow the rover’s decent even further.
Once it was sufficiently close to the surface, the Sky Crane lowed the rover to the ground with tethers measuring 6.4 meters (21 ft) long. It then detached and landed a safe distance away, not far from the Descent module’s heat shield, backshell, and parachute landed. These jettisoned bits were all photographed from orbit by the MSL’s HiRISE instrument a day after the landing.
Unfortunately, this kind of technology does not address another major concern – which is the accumulation of spent hardware components on the surface of a planet. In time, these could pose risks for future missions, mainly because they have the potential of being blown around and cluttering up other (and future) landing sites that are located not far away.
Artist’s impression of the Mars 2020 with its sky crane landing system deployed. Credit: NASA/JPL
As Dr. Paton indicated in an interview with Seeker columnist (and Universe Today alumnist) Elizabeth Howell:
“Currently available landing systems, using heat shield and parachutes, might be problematic because jettisoned hardware from these landers normally land within a few hundred meters of the lander. I would imagine a sample return mission would not jettison its parachute in close vicinity of the target sample or the cached sample. The parachute might cover the sample, making its retrieval a problem. Landers using large parachutes or other large devices probably pose the greatest risk as these could be easily blown onto equipment on the surface, damaging or covering it.”
For the sake of his study, Dr. Paton relied on 3D computer modelling (using the space flight simulator Orbiter) to examine different types of ELD systems. He then conducted meteorological measurements to determine wind speeds and direction within the Martian Planetary Boundary Layer (PBL), in order to determine their influence on the distribution of jettisoned components across the surface of Mars.
What he found was that winds speeds within the Martian PBL were sufficient enough to blow around certain types of EDL systems. This included parachutes – a mainstay of space missions – as well as next-generations concepts like the HIAC. Basically, these components could be blown onto prelanded assets, even when the lander itself has touched down several kilometers away.
This could play havoc with robotic missions that have sensitive equipment or are attempting to collect samples for return to Earth. And as for crewed missions – such as NASA’s proposed “Journey to Mars”, which is expected to take place in the 2030s – the results could be even worse. Crew habitats, which will be part of all future crewed missions, will rely on solar panels and other devices that need to be free of clutter in order to function.
Artist’s concept of the Deceleration module of Mars Science Laboratory in entering the Martian Atmosphere. Credit: NASA/JPL-Caltech
As such, Dr. Paton advises that future missions be designed so that the amount of hardware they leave behind is minimized. In addition, he advises that any future missions will need to take into account meteorological measurement to make sure that jettisoned components are not likely to blow back and interfere with missions in progress.
“For new landing systems, a detailed trade-off analysis would be required to determine the best way to mitigate this problem,” he said. “To be sure that the wind is blowing away from any landed assets, the winds in the lower few kilometers of the atmosphere would ideally need to be measured close to the time of the lander’s expected arrival.”
As if planning missions to Mars wasn’t already challenging enough! In addition to all the things we need to worry about in getting there, now we need to worry about keeping our landing sites in pristine order. But of course, such considerations are understandable since our presence on Mars is expanding, and many key missions are planned for the coming years.
These include more robotic rovers in the next decade – i.e NASA’s Mars 2020 rover, the ESA’s Exomars rover, and the ISRO’s Mangalyaan 2 rover – an even NASA’s proposed “Journey to Mars” by the 2030s. If we’re going to make Mars a regular destination, we need to learn to pick up after ourselves!
Approximately every two years, Earth and Mars are at the closest point to each other in their orbits (i.e. opposition). Credit: NASA
As neighboring planets, Earth and Mars have a few things in common. Both are terrestrial in nature (i.e. rocky), both have tilted axes, and both orbit the Sun within its circumstellar habitable zone. And during the course of their orbital periods (i.e. a year), both planets experience variations in temperature and changes in their seasonal weather patterns.
However, owing to their different orbital periods, a year on Mars is significantly longer than a year on Earth – almost twice as long, in fact. And because their orbits are different, the distance between our two planets varies considerably. Basically, every two years Earth and Mars will go from being “at conjunction” (where they are farther from each other) to being “at opposition” (where they are closer to each other).
Orbital Period:
Earth orbits the Sun at an average distance (semi-major axis) of 149,598,023 km (92,955,902 mi; or 1 AU), ranging from 147,095,000 km (91,401,000 mi) at perihelion to 152,100,000 km (94,500,000 mi) at aphelion. At this distance, and with an orbital velocity of 29.78 km/s (18.5 mi/s) the time it take for the planet to complete a single orbit of the Sun (i.e. orbital period) is equal to about 365.25 days.
A top-down image of the orbits of Earth and Mars. Credit: NASA
Mars, meanwhile, orbits the Sun at an average distance of 227,939,200 km (141,634,850 mi; or 1.523679 AU), ranging from 206,700,000 km (128,437,425 mi) at perihelion to 249,200,000 km (154,845,700 mi) at aphelion. Given this difference in distance, Mars orbits the Sun at a slower speed (24.077 km/s; 14.96 mi/s) and takes about 687 Earth days (or 668.59 Mars sols) to complete a single orbit.
In other words, a Martian year is almost 700 days long, which works out to being 1.88 times as long as a year on Earth. This means that every time Mars completes a single orbit around the Sun, the Earth has gone around almost twice. During the moments when they are on opposite sides of the Sun, this is known as a “conjunction”. When they are on the same side of the Sun, they are at “opposition”.
Mars Opposition:
By definition, a “Mars opposition” occurs when planet Earth passes in between the Sun and planet Mars. The term refers to the fact that Mars and the Sun appear on opposite sides of the sky. Because of their orbits, Mars oppositions happens about every 2 years and 2 months – 779.94 Earth days to be precise. From our perspective here on Earth, Mars appears to be rising in the east just as the Sun sets in the west.
About every two years, the Earth passes Mars as they orbit around the Sun. Credit: NASA
After staying up in the sky for the entire night, Mars then sets in the west just as the Sun begins to rise in the east. During an opposition, Mars becomes one of the brightest objects in the night sky, and is easy to see with the naked eye. Through small telescopes, it will appear as a large and bright object. Through larger telescopes, Mars’ surface features will even become apparent, which would include its polar ice caps.
An opposition can also occur anywhere along Mars’ orbit. However, opposition does not necessary mean that the two planets are at their closest overall. In truth, it just means that they are are at their closest point to each other within their current orbital period. If Earth and Mars’ orbits were perfectly circular, they would be closest to each other whenever they were at opposition.
Instead, their orbits are elliptical, and Mars’ orbit is more elliptical than Earth’s – which means the difference between their respective perihelion and aphelion is greater. Gravitational tugging from other planets constantly changes the shape of our orbits too – with Jupiter pulling on Mars and Venus and Mercury affecting Earth.
Color composite of Mars from seven of its previous oppositions, taken with the Hubble Space Telescope. Credit: NASA/ESA/HST
Lastly, Earth and Mars do not orbit the Sun on the exact same plane – i.e. their orbits are slightly tilted relative to each other. Because of this, Mars and Earth become closest to each other only over the long-term. For instance, every 15 or 17 years, an opposition will occur within a few weeks of Mars’ perihelion. When it happens while the Mars is closest to the sun (called “perihelic opposition”), Mars and Earth get particularly close.
And yet, the closest approaches between the two planets only take place over the course of centuries, and some are always closer than others. To make matters even more confusing, over the past few centuries, Mars’ orbit has been getting more and more elongated, carrying the planet even nearer to the Sun at perihelion and even farther away at aphelion. So future perihelic oppositions will bring Earth and Mars even closer.
On August 28th, 2003, astronomers estimated that Earth and Mars were just 55,758,118 km (34,646,488 mi; 0.37272 AU) apart. This was the closest the two planets had come to each other in almost 60,000 years. This record will stand until August 28th, 2287, at which point the planets will be an estimated 55,688,405 km (34,603,170.6 mi; 0.372254 AU) from each other.
Future Oppositions:
Want to organize your schedule for the next time Mars will be close to Earth? Here are some upcoming dates, covering the next few decades. Plan accordingly!
July 27th, 2018
October 13th, 2020
December 8th, 2022
January 16th, 2025
February 19th, 2027
Mar 25th, 2029
May 4th, 2031
June 27th, 2033
September 15th, 2035
November 19th, 2037
January 2nd, 2040
February 6th, 2042
March 11th, 2044
April 17th, 2046
June 3rd, 2048
August 14th, 2050
And in case your interested, Mars will be making close approaches on two occasions this century. The first will take place on August 14th, 2050, when Mars and Earth will be 55.957 million km (34.77 million mi; or 0.374051 AU) apart; and on September 1st, 2082, when they will be 55,883,780 km (34,724,571 mi; 0.373564 AU) apart.
There’s a reason missions to Mars depart from Earth every two years. Seeking to take advantage of shorter travel times, rovers, orbiters and landers are launched to coincide with Mars being at opposition. And when it comes time to send crewed mission to Mars (or even settlers) the same timing will apply!
This image is a mosaic of all the images captured by the Context Camera (CTX) on NASA's Mars Reconnaissance Orbiter. The CTX has imaged over 99% of the Martian surface. Image: NASA/JPL-Caltech/MSSS
Most of us never do one thing 50,000 times in our life. So for NASA’s Mars Reconnaissance Orbiter (MRO), completing 50,000 orbits around the red planet is a big deal. And, it only took 10 years to do so.
The MRO could be called one of NASA’s flagship missions. It’s presence in orbit around Mars has helped open up our understanding of that planet immensely. And it’s done so while providing us a steady stream of eye candy.
This recent image from MRO’s HiRise camera shows dune structure inside an impact crater. Image: NASA/JPL/University of Arizona
MRO was launched in 2005 and reached Mars orbit in March, 2006. After 10 years at work, it has accomplished a lot. In a recent press release, NASA calls the MRO “the most data-productive spacecraft yet.” Though most of us might know the orbiter because of it’s camera, the High-Resolution Imaging Science Experiment (HiRise), the MRO actually has a handful of other instruments that help the orbiter achieve its objectives. In broad terms, those objectives are:
to study the history of water on Mars
to look at small scale features on the surface, and identify landing sites for future Mars missions
to act as a communications relay between Mars and Earth
MRO investigating Martian water cycle – This artist’s concept represents the “Follow the Water” theme of NASA’s Mars Reconnaissance Orbiter mission. The orbiter’s science instruments monitor the present water cycle in the Mars atmosphere and the associated deposition and sublimation of water ice on the surface, while probing the subsurface to see how deep the water-ice reservoir extends. Image: By NASA/JPL/Corby Waste – http://photojournal.jpl.nasa.gov/catalog/PIA07241 (image link), Public Domain, https://commons.wikimedia.org/w/index.php?curid=374810 (Larger image here.
MRO’s HiRise camera gets all the glory, but it’s another onboard camera, the Context Camera (CTX), that is the real workhorse. The CTX is a much lower resolution than the HiRise, but its file sizes are much more manageable, an important consideration when every file has to travel from Mars to Earth—an average distance of about 225 million km.
CTX has captured 90,000 images so far in MRO’s mission, and each one captures details smaller than a tennis court. In the course of the mission so far, CTX has images that cover 99.1% of the Martian surface. Over 60% of the planet has been covered twice.
“Reaching 99.1-percent coverage has been tricky…” – Context Camera Team Leader Michael Malin
“Reaching 99.1-percent coverage has been tricky because a number of factors, including weather conditions, coordination with other instruments, downlink limitations, and orbital constraints, tend to limit where we can image and when,” said Context Camera Team Leader Michael Malin of Malin Space Science Systems, San Diego.
Malin said, “Single coverage provides a baseline we can use for comparison with future observations, as we look for changes. Re-imaging areas serves two functions: looking for changes and acquiring stereoscopic views from which we can make topographic maps.”
Because the CTX captures image of the same surface areas twice, it documents changes on the surface. There have been over 200 instances of impact craters appearing in a second image of the same area. Scientists have used this to calculate the rate that meteorites impact Mars.
The instruments on board the MRO work as a team. The CTX can capture images of areas of interest, and the HiRise can be used for higher-resolution images of the same area. By locating fresh impact craters, then studying them more closely, the MRO has helped discover the presence of what looked like sub-surface ice on Mars. A third instrument, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), confirmed the presence of ice.
The CTX is the workhorse camera, and the HiRise is the diva, but MRO actually has a third camera: the Mars Color Imager (MARCI). MARCI is a very low resolution camera compared to the others. It’s also a wide-angle camera with really only one purpose: characterizing Martian weather. Every day, MARCI takes about 84 images which together create a daily global map of Mars. You can see a weekly Martian weather report from MARCI here.
The MRO recently manoeuvered itself into position for its next task—helping the InSight Lander. The MRO must receive critical radio transmissions from NASA’s InSight Lander as it descends to Mars. Insight will use its instruments to examine the interior of Mars for clues to how rocky planets form. Not only did MRO help find a landing spot for Insight, but it will hold the lander’s hand as it descends, and it will act as a data relay.
“After 11 and a half years in flight, the spacecraft is healthy and remains fully functional.” – MRO Project Manager Dan Johnston.
There’s no end in sight for the MRO. It just keeps going and going, and fulfilling its mission objectives on a continuing basis. “After 11 and a half years in flight, the spacecraft is healthy and remains fully functional,” said MRO Project Manager Dan Johnston at NASA’s Jet Propulsion Laboratory, Pasadena, California. “It’s a marvelous vehicle that we expect will serve the Mars Exploration Program and Mars science for many more years to come.”
Beads of rainwater on a poplar leaf act like lenses, focusing light and enlarging the leaf’s network of veins. Moving at 186,000 miles per second, light from the leaf arrives at your eye 0.5 nanosecond later. A blink of an eye takes 600,000 times as much time! Credit: Bob King
My attention was focused on beaded water on a poplar leaf. How gemmy and bursting with the morning’s sunlight. I moved closer, removed my glasses and noticed that each drop magnified a little patch of veins that thread and support the leaf.
Focusing the camera lens, I wondered how long it took the drops’ light to reach my eye. Since I was only about six inches away and light travels at 186,000 miles per second or 11.8 inches every billionth of a second (one nanosecond), the travel time amounted to 0.5 nanoseconds. Darn close to simultaneous by human standards but practically forever for positronium hydride, an exotic molecule made of a positron, electron and hydrogen atom. The average lifetime of a PsH molecule is just 0.5 nanoseconds.
Light takes about 35 microseconds to arrive from a transcontinental jet and its contrail. Credit: Bob King
In our everyday life, the light from familiar faces, roadside signs and the waiter whose attention you’re trying to get reaches our eyes in nanoseconds. But if you happen to look up to see the tiny dark shape of a high-flying airplane trailed by the plume of its contrail, the light takes about 35,000 nanoseconds or 35 microseconds to travel the distance. Still not much to piddle about.
The space station orbits the Earth in outer space some 250 miles overhead. During an overhead pass, light from the orbiting science lab fires up your retinas 1.3 milliseconds later. In comparison, a blink of the eye lasts about 300 milliseconds (1/3 of a second) or 230 times longer!
The Lunar Laser Ranging Experiment placed on the Moon by the Apollo 14 astronauts. Observatories beam a laser to the small array, which reflects a bit of the light back. Measuring the time delay yields the Moon’s distance to within about a millimeter. At the Moon’s surface the laser beam spreads out to 4 miles wide and only one photon is reflected back to the telescope every few seconds. Credit: NASA
Light time finally becomes more tangible when we look at the Moon, a wistful 1.3 light seconds away at its average distance of 240,000 miles. To feel how long this is, stare at the Moon at the next opportunity and count out loud: one one thousand one. Retroreflecting devices placed on the lunar surface by the Apollo astronauts are still used by astronomers to determine the moon’s precise distance. They beam a laser at the mirrors and time the round trip.
Venus as a super-thin crescent only 10 hours before conjunction on March 25. The planet was just 2.3 light minutes from the Earth at the time. Credit: Shahrin Ahmad
Of the eight planets, Venus comes closest to Earth, and it does so during inferior conjunction, which coincidentally occurred on March 25. On that date only 26.1 million miles separated the two planets, a distance amounting to 140 seconds or 2.3 minutes — about the time it takes to boil water for tea. Mars, another close-approaching planet, currently stands on nearly the opposite side of the Sun from Earth.
With a current distance of 205 million miles, a radio or TV signal, which are both forms of light, broadcast to the Red Planet would take 18.4 minutes to arrive. Now we can see why engineers pre-program a landing sequence into a Mars’ probe’s computer to safely land it on the planet’s surface. Any command – or change in commands – we might send from Earth would arrive too late. Once a lander settles on the planet and sends back telemetry to communicate its condition, mission control personnel must bite their fingernails for many minutes waiting for light to limp back and bring word.
Before we speed off to more distant planets, let’s consider what would happen if the Sun had a catastrophic malfunction and suddenly ceased to shine. No worries. At least not for 8.3 minutes, the time it takes for light, or the lack of it, to bring the bad news.
Pluto and Charon lie 3.1 billion miles from Earth, a long way for light to travel. We see them as they were more than 4 hours ago. NASA/JHUAPL/SwRI
Light from Jupiter takes 37 minutes to reach Earth; Pluto and Charon are so remote that a signal from the “double planet” requires 4.6 hours to get here. That’s more than a half-day of work on the job, and we’ve only made it to the Kuiper Belt.
Let’s press on to the nearest star(s), the Alpha Centauri system. If 4.6 hours of light time seemed a long time to wait, how about 4.3 years? If you think hard, you might remember what you were up to just before New Year’s Eve in 2012. About that time, the light arriving tonight from Alpha Centauri left that star and began its earthward journey. To look at the star then is to peer back in time to late 2012.
The Summer Triangle rises fully in the eastern sky around 3 o’clock in the morning in late March. Created with Stellarium
But we barely scrape the surface. Let’s take the Summer Triangle, a figure that will soon come to dominate the eastern sky along with the beautiful summer Milky Way that appears to flow through it. Altair, the southernmost apex of the triangle is nearby, just 16.7 light years from Earth; Vega, the brightest a bit further at 25 and Deneb an incredible 3,200 light years away.
We can relate to the first two stars because the light we see on a given evening isn’t that “old.” Most of us can conjure up an image of our lives and the state of world affairs 16 and 25 years ago. But Deneb is exceptional. Photons departed this distant supergiant (3,200 light years) around the year 1200 B.C. during the Trojan War at the dawn of the Iron Age. That’s some look-back time!
Rho Cassiopeia, currently at magnitude +4.5, is one of the most distant stars visible with the naked eye. Its light requires about 8,200 years to reach our eyes. This star, a variable, is enormous with a radius about 450 times that of the Sun. Credit: IAU/Sky and Telescope (left); Anynobody, CC BY-SA 3.0 / Wikipedia
One of the most distant naked eye stars is Rho Cassiopeiae, yellow variable some 450 times the size of the Sun located 8,200 light years away in the constellation Cassiopeia. Right now, the star is near maximum and easy to see at nightfall in the northwestern sky. Its light whisks us back to the end of the last great ice age at a time and the first cave drawings, more than 4,000 years before the first Egyptian pyramid would be built.
This is the digital message (annotated here) sent by Frank Drake to M13 in 1974 using the Arecibo radio telescope.
On and on it goes: the nearest large galaxy, Andromeda, lies 2.5 million light years from us and for many is the faintest, most distant object visible with the naked eye. To think that looking at the galaxy takes us back to the time our distant ancestors first used simple tools. Light may be the fastest thing in the universe, but these travel times hint at the true enormity of space.
Let’s go a little further. On November 16, 1974 a digital message was beamed from the Arecibo radio telescope in Puerto Rico to the rich star cluster M13 in Hercules 25,000 light years away. The message was created by Dr. Frank Drake, then professor of astronomy at Cornell, and contained basic information about humanity, including our numbering system, our location in the solar system and the composition of DNA, the molecule of life. It consisted of 1,679 binary bits representing ones and zeroes and was our first deliberate communication sent to extraterrestrials. Today the missive is 42 light years away, just barely out the door.
Galaxy GN-z11, shown in the inset, is seen as it was 13.4 billion years in the past, just 400 million years after the big bang, when the universe was only three percent of its current age. The galaxy is ablaze with bright, young, blue stars, but looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe. Credit: NASA, ESA, P. Oesch, G. Brammer, P. van Dokkum, and G. Illingworth
Let’s end our time machine travels with the most distant object we’ve seen in the universe, a galaxy named GN-z11 in Ursa Major. We see it as it was just 400 million years after the Big Bang (13.4 billion years ago) which translates to a proper distance from Earth of 32 billion light years. The light astronomers captured on their digital sensors left the object before there was an Earth, a Solar System or even a Milky Way galaxy!
Thanks to light’s finite speed we can’t help but always see things as they were. You might wonder if there’s any way to see something right now without waiting for the light to get here? There’s just one way, and that’s to be light itself.
From the perspective of a photon or light particle, which travels at the speed of light, distance and time completely fall away. Everything happens instantaneously and travel time to anywhere, everywhere is zero seconds. In essence, the whole universe becomes a point. Crazy and paradoxical as this sounds, the theory of relativity allows it because an object traveling at the speed of light experiences infinite time dilation and infinite space contraction.
Just something to think about the next time you meet another’s eyes in conversation. Or look up at the stars.
Mercury requests the company of your gaze now through the beginning of April, when it shines near Mars low in the west after sunset. Created with Stellarium
March has been a busy month for planet and comet watchers. Lots of action. Venus, the planet that’s captured our attention at dusk in the west for months, is in inferior conjunction with the Sun today. Watch for it to rise before the Sun in the eastern sky at dawn in about a week.
Mercury like Venus and the Moon shows phases when viewed through a telescope. Right now, the planet is in waning gibbous phase. Stellarium
As Venus flees the evening scene, steadfast Mars and a new planet, Mercury keep things lively. For northern hemisphere skywatchers, this is Mercury’s best dusk apparition of the year. If you’d like to make its acquaintance, this week and next are best. And it’s so easy! Just find a spot with a wide open view of the western horizon, bring a pair of binoculars for backup and wait for a clear evening.
Plan to watch starting about 40 minutes after sundown. From most locations, Mercury will appear about 10° or one fist held at arm’s length above the horizon a little bit north of due west. Shining around magnitude +0, it will be the only “star” in that part of the sky. Mars is nearby but much fainter at magnitude +1.5. You’ll have to wait at least an hour after sunset to spot it.
Have a telescope? Check out the planet using a magnification around 50x or higher. You’ll see that it looks like a Mini-Me version of the Moon. Mercury is brightest when closest to full. Over the next few weeks, it will wane to a crescent while increasing in apparent size.
If you have any difficulty finding brilliant Jupiter and its current pal, Spica, just start with the Big Dipper, now high in the northeastern sky at nightfall. Use the Dipper’s handle to “arc to Arcturus” and then “jump to Jupiter.” Credit: Bob King
If you like planets, don’t forget the combo of Jupiter and Spica at the opposite end of the sky. Jupiter climbs out of bed and over the southeastern horizon about 9 p.m. local time in late March, but to see it and Spica, Virgo’s brightest star, give it an hour and look again at 10 p.m. or later. Quite the duo!
You’re not afraid of getting up with the first robins are you? If you set your alarm to a half hour or so before the first hint of dawn’s light and find a location with an open view of the southeastern horizon, you might be first in your neighborhood to spot Terry Lovejoy’s brand new comet. His sixth, the Australian amateur discovered C/2017 E4 Lovejoyon the morning of March 10th in the constellation Sagittarius at about 12th magnitude.
C/2017 E4 Lovejoy glows blue-green this morning March 26. Structure around the nucleus including a small jet is visible. The comet is currently in Aquarius and quickly moving north and will reach perihelion on April 23. Credit: Terry Lovejoy
The comet has rapidly brightened since then and is now a small, moderately condensed fuzzball of magnitude +9, bright enough to spot in a 6-inch or larger telescope. Some observers have even picked it up in large binoculars. Lovejoy’s comet should brighten by at least another magnitude in the coming weeks, putting it within 10 x 50 binocular range.
This map shows the sky tomorrow morning before dawn from the central U.S. (latitude about 41° north). Created with Stellarium
Good news. E4 Lovejoy is moving north rapidly and is now visible about a dozen degrees high in Aquarius just before the start of dawn. I’ll be out the next clear morning, eyepiece to eye, to welcome this new fuzzball from beyond Neptune to my front yard. The map above shows the eastern sky near dawn and a general location of the comet. Use the more detailed map below to pinpoint it in your binoculars and telescope.
This chart shows the comet’s position nightly (5:30 a.m. CDT) through April 9. On the morning of April 1 it passes just a few degrees below the bright globular cluster M15. Click to enlarge, save and then print out for use at the telescope. Map: Bob King, Source: Chris Marriott’s SkyMap
Spring brings with it a new spirit and the opportunity to get out at night free of the bite of mosquitos or cold. Clear skies!
Mars, as photographed with the Mars Global Surveyor, is identified with the Roman god of war. Credit: NASA
This week, from March 20th to 24th, the 48th Lunar and Planetary Science Conference will be taking place in The Woodlands, Texas. Every year, this conference brings together international specialists in the fields of geology, geochemistry, geophysics, and astronomy to present the latest findings in planetary science. One of the highlights of the conference so far has been a presentation about Mars’ weather patterns.
When it comes to cloud formations, gravity waves are the result of gravity trying to restore them to their natural equilibrium. And while common on Earth, such formation were not thought to be possible around Mars’ equatorial band, where the gravity waves were seen. All of this was made possible thanks to Curiosity’s advantageous position inside the Gale Crater.
Panoramic image showing cirrus clouds in the Martian atmosphere, taken by the Opportunity rover in 2006. Credit: NASA/JPL/Cornell/M. Howard, T. Öner, D, Bouic & M. Di Lorenzo
Located near Mars’ equator, Curiosity has managed to consistently record what is known as the Aphelion Cloud Belt (ACB). As the name would suggest, this annually-recurring phenomena appears during the aphelion season on Mars (when it is farthest from the Sun) between the latitudes of 10°S and 30°N. During aphelion, the point farthest from the Sun, the planet is dominated by two cloud systems.
These include the aforementioned ACB, and the polar phenomena known as Polar Hood Clouds (PHCs). Whereas PHCs are characterized by clouds of carbon dioxide, clouds that form around Mars’ equatorial band are made up water-ice. These cloud systems them dissipate as Mars gets closer to the Sun (perihelion), where increases in temperature lead to the creation of dust storms that limit cloud formation.
During the nearly five years that Curiosity has been operational, the rover has recorded over 500 movies of the equatorial Martian sky. These movies have taken the form of both Zenith Movies (ZMs) – which involve the camera being pointed vertically – and Supra-Horizon Movies (SHM), which were aimed at a lower angle of elevation to keep the horizon in frame.
Using Curiosity’s navigation camera, Jacob Kloos and Dr. John Moores – two researchers from CRESS – made eight recordings of the ACB over the course of two Martian years – specifically between Mars Years 31 and Mars Years 33 (ca. 2012 to 2016). By comparing ZM and SHM movies, they were able to discern changes in the clouds that were both diurnal (daily) and annual in nature.
What they found was that between 2015 and 2016, Mars’ ACB underwent changes in opacity (aka. changes in density) during its diurnal cycle. After periods of enhanced early morning activity, the clouds would reach a minimum by late morning. This is followed by a second, lower peak in the late afternoon, which indicated that Mars’ early morning hours are the most favorable time for the formation of thicker clouds.
Hubble images show cloud formations (left) and the effects of a global dust storm on Mars. Credit: NASA/James Bell (Cornell Univ.), Michael Wolff (Space Science Inst.), and Hubble Heritage Team (STScI/AURA)
As for inter-annual variability, they found that between 2012 and 2016, when Mars moved away from aphelion, there was a corresponding 38% increase in the number of higher-opacity clouds. However, believing these results to be the result of a statistical bias caused by an uneven distribution of videos, they concluded that the difference in opacity was more along the lines of about 5%.
These variations were all of this is consistent with tidal temperature variations, where cooler daytime or seasonal temperatures result in greater levels of condensation in the air. The trend of increasing clouds throughout the day was unexpected, however, as higher temperatures should lead to a decrease in saturation. However, as they explained during their presentation, this too could be attributed to daily changes:
“One explanation for the afternoon enhancement put forth by Tamppari et. al. is that as atmospheric temperatures increase the throughout the day, enhanced convection lifts water vapor to the saturation altitude, therefore increasing the likelihood of cloud formation. In addition to water vapor, dust could also be lifted, which act as condensation nuclei, allowing for more efficient cloud formation.”
However, what was most interesting was the fact that during one of day of observation – Sol 1302, or April 5th, 2016 – the team managed to observe something surprising. When looking at the horizon during an SHM, the NavCam caught sight of parallel rows of clouds which all pointed in the same direction. While such ripples are known to happen in the polar regions (where PHCs are concerned), spotting them over the equator was unexpected.
Sunset photographed from Gale Crater by the Mars Curiosity rover on April 15, 2015 taken using the left eye of the rover’s Mastcam. Credit: NASA/JPL-Caltec
But as Moore explained in an interview with Science Magazine,seeing an Earth-like phenomenon on Mars is consistent with what we’ve seen so far from Mars. “The Martian environment is the exotic wrapped in the familiar,” he said. “The sunsets are blue, the dust devils enormous, the snowfall more like diamond dust, and the clouds are thinner than what we see on the Earth.”
At present, it is not clear which mechanism could be responsible for creating these ripples in the first place. On Earth, they are caused by disturbances below in the troposphere, solar radiation, or jet stream sheer. Knowing what could account for them on Mars will likely reveal some interesting things about its atmosphere’s dynamics. At the same time, further research is necessary before scientists can say definitely that gravity waves were observed here.
But in the meantime, these findings are fascinating, and are sure to help advance our knowledge of the Red Planet’s atmosphere and the water cycle on Mars. As ongoing research has shown, Mars still experiences flows of liquid salt water on its surface, and even experiences limited precipitation. And in telling us more about Mars’ present-day meteorology, it could also reveal things about the planet’s watery past.
To see the recordings of Martian clouds, click here,here and here.
Image taken by the Mars Hand Lens Imager (MAHLI) of Curiosity's wheels on March 19, 2017. Credit: NASA
Since it landed on August 6th, 2012, the Curiosityrover has spent a total of 1644 Sols (or 1689 Earth days) on Mars. And as of March 2017, it has traveled almost 16 km (~10 mi) across the planet and climbed almost a fifth of a kilometer (0.124 mi) uphill. Spending that kind of time on another planet, and traveling that kind of distance, can certainly lead to its share of wear of tear on a vehicle.
That was the conclusion when the Curiosity science team conducted a routine check of the rover’s wheels on Sunday, March 19th, 2017. After examining images taken by the Mars Hand Lens Imager (MAHLI), they noticed two small breaks in the raised treads on the rover’s left middle wheel. These breaks appeared to have happened since late January, when the last routine check of the wheels took place.
To get around, the Curiosity rover relies on six solid aluminum wheels that are 40 cm (16 in) wide. The skin of the wheels is thinner than a US dime, but each contains 19 zigzag-shaped treads that are about 0.75 cm (three-quarters of an inch) thick. These “grousers”, as they are called, bear most of the rover’s weight and provide most of the wheel’s traction.
Close-up image of the broken grousers on Curiosity’s left-middle wheel. Credit: NASA/JPL-Caltech/MSSS
Ever since the rover was forced to cross a stretch of terrain that was studded with sharp rocks in 2013, the Curiosity team has made regular checks on the rover’s wheels using the MAHLI camera. At the time, the rover was moving from the Bradbury Landing site (where it landed in 2012) to the base of Mount Sharp, and traversing this terrain caused holes and dents in the wheels to grow significantly.
However, members of Curiosity’s science team emphasized that this is nothing to be worried about, as it will not affect the rover’s performance or lifespan. As Jim Erickson, the Curiosity Project Manager at NASA’s Jet Propulsion Laboratory, said in a recent NASA press statement:
“All six wheels have more than enough working lifespan remaining to get the vehicle to all destinations planned for the mission. While not unexpected, this damage is the first sign that the left middle wheel is nearing a wheel-wear milestone.”
In addition to regular monitoring, a wheel-longevity testing program was started on Earth in 2013 using identical aluminum wheels. These tests showed that once a wheel got to the point where three of its grousers were broken, it had passed about 60% of its lifespan. However, Curiosity has already driven more than 60% of the total distance needed for it to make it to all of its scientific destinations.
Graphic depicting aspects of the driving distance, elevation, geological units and time intervals of NASA’s Curiosity Mars rover mission, as of late 2016. Credit: NASA/JPL-Caltech
“This is an expected part of the life cycle of the wheels and at this point does not change our current science plans or diminish our chances of studying key transitions in mineralogy higher on Mount Sharp.”
At present, Curiosity is examining sand dunes in the geographical region known as the Murray Buttes formation, which is located on the slope of Mount Sharp. Once finished, it will proceed up higher to a feature known as “Vera Rubin Ridge”, inspecting a layer that is rich in the mineral hematite. From there, it will proceeded to even higher elevations to inspect layers that contain clays and sulfates.
Getting to the farthest destination (the sulfate unit) will require another 6 km (3.7 mi) of uphill driving. However, this is a short distance compared to the kind of driving the rover has already performed. Moreover, the science team has spent the past four years implementing various methods designed to avoid embedded rocks and other potentially hazardous terrain features.
MRO image of Gale Crater illustrating the landing location and trek of the Rover Curiosity. Credits: NASA/JPL, illustration, T.Reyes
It is expected that this drive up Mount Sharp will yield some impressive scientific finds. During its first year on Mars, Curiosity succeeded in gathering evidence in the Gale Crater that showed how Mars once had conditions favorable to life. This included ample evidence of liquid water, all the chemical elements needed for life, and even a chemical source of energy.
By scaling Mount Sharp and examining the layers that were deposited over the course of billions of years, Curiosity is able to examine a living geological record of how the planet has evolved since then. Luckily, the rover’s wheels seem to have more than enough life to make these and (most likely) other scientific finds.
An artist's illustration of SpaceX's Dragon capsule entering the Martian atmosphere. Image: SpaceX
As part of their effort to kick-start the eventual colonization of Mars, SpaceX is sending an unmanned Dragon spacecraft to Mars. Initially, that mission was set for 2018, but is now re-scheduled for 2020. Now, SpaceX says they’re working with NASA to select a suitable landing site for their first Dragon mission to Mars.
At a presentation in Texas on March 18th, Paul Wooster of SpaceX said that they have been working with scientists at NASA’s Jet Propulsion Laboratory (JPL) to identify candidate landing sites on the surface of Mars. In order to aid colonization, the sites need to be:
near the equator, for solar power
near large quantities of ice, for water
at low elevation, for better thermal conditions
But finding a site that meets those conditions is difficult.
According to SpaceNews, the study done with NASA initially recognized 4 regions in Mars’ northern hemisphere, all within 40 degrees of the equator. They are Deuteronilus Mensae, Phlegra Montes, Utopia Planitia, and Arcadia Planitia.
Deuteronilus Mensae
Deuteronilus Mensae (DM) is located between older, cratered highlands and low plains. DM shows evidence of glacial activity in its surface features. In fact, there are still glaciers there, which makes it a desirable source of ice.
Deuteronilus Mensae (DM)has many rough surface features. The Mars Reconnaissance Orbiter has shown that many areas in DM are sub-surface glaciers covered by a thin layer of debris. Image: NASA/JPL/University of Arizona
Phlegra Montes
Phlegra Montes (PM) is a system of mountains on the Martian surface, over 1300 km across. It’s a complex system of basins, hills, and ridges. They are likely tectonic in origin, rather than volcanic, and the region probably contains large quantities of water ice, perhaps 20 meters below the surface.
This tongue shaped flow of material at Phlegra Montes may have been formed by a flow of ice-rich material. Image: NASA/JPL/University of Arizona
Utopia Planitia
Utopia Planitia (UP) is the region where the Viking 2 lander set down in 1976. At 3300 km in diameter, UP is the largest impact basin in the Solar System. In 2016, NASA found a huge deposit of underground ice there. The water is estimated to be the same volume as Lake Superior.
Periglacial features in a small crater in Utopia Planitia. Periglacial refers to the seasonal thawing of snow and ice which refreezes in other shapes. Image: NASA/JPL/University of Arizona
Arcadia Planitia
Arcadia Planitia (AP) is a smooth plain containing fresh lava flows. It also has a large region that was shaped by periglacial processes. This supports the idea that ice is present just beneath the surface, making it a candidate for colonization efforts.
Arcadia Planitia likely has ice just beneath its surface. The knobby pattern is probably caused by the uneven seasonal melting of sub-surface ice. Image: NASA/JPL/University of Arizona
The image below shows the Arcadia Planitia region in relation to some of its surroundings. Colonists at AP might have a great view of Olympus Mons, the largest volcano in the Solar System.
Colonists in Arcadia Planitia (upper left in map) might have a great view of Olympus Mons.
The four areas looked suitable in images from a medium resolution camera (CTX) on the Mars Reconnaissance Orbiter (MRO). But when the High Resolution Imaging Science Experiment (HiRISE) camera on the same orbiter was used to look more closely, the first three locations appeared to be much rockier. According to SpaceNews, Wooster said ““The team at JPL has been finding that, while the areas look very flat and smooth at CTX resolution, with HiRISE images, they’re quite rocky. That’s been unfortunate in terms of the opportunities for those sites.”
The fourth area, Arcadia Planitia, is a more promising site. HiRISE images showed that it is much less rocky and could be a suitable site for the first Dragon mission to Mars.
The Dragon mission to Mars is just the first step for SpaceX. They see themselves as an interplanetary transportation company eventually. SpaceX intends to send a craft to Mars every two years, when the launch window is optimal. SpaceX says they’ll have the ability to deliver one ton of payload to the Martian surface with each Dragon mission.
Their Interplanetary Transport System (ITS) might have the capability to make it to Mars in as little as 80 days, while carrying a payload of up to 450 tons. While still in the very initial stages of design, it may eventually revolutionize our ability to colonize Mars in any meaningful or enduring way. SpaceX envisions a fleet of craft in the ITS which will constantly make the return to trip to Mars.
If that ever happens, we may look at the first Dragon mission to Arcadia Planitia, or another eventual landing site, as the first step.
