Sunday, May 29, 2022

Science is for all of us!


 This week on the PVL Blog Post, MSc student Ankita talks about citizen science, a way by which anyone can participate in scientific research and discovery.
Image Above: YorkU Galaxified Generate your own text at: http://writing.galaxyzoo.org/

By Ankita Das

Being someone who developed a keen interest in science at a very early age I was always looking for new ways to learn and contribute to the science happening in the world. By the time I was in my early teens, citizen science projects were my favorite way to spend time when I was not involved in academic work. I spent my winter of 2010 sending my friends and family a personalized season’s greetings. Except, there was something special about these messages – the text was “galaxified” using GalaxyZoo’s special tool where each letter was a galaxy from the Sloan Digital Sky Survey (SDSS). These were the little ways I would incorporate space into my daily life. But my love for science at that age went beyond generating cute galaxified texts.


Citizen science is often someone’s first introduction to hands-on science. Personally, my first citizen science projects were in Galaxy Zoo and Planet Hunters by Zooniverse. The Galaxy Zoo project involved classifying galaxies into categories by looking at its shape - something even a child can do but holds valuable science behind the activity. A lot can be revealed about a galaxy just from its shape. For example, an elliptical galaxy is usually an old galaxy where no active star formation takes place and spiral arms in a galaxy imply a rotating disk of stars. The shape classification were according to Hubble’s classification scheme shown in image 2.

 

Image 2: Hubble’s Classification Scheme for galaxies (Source: Wikipedia Commons)

Apart from classifying galaxies imaged by SDSS, my other favorite go-to project involved looking at light curves from distant exoplanets being discovered by Kepler. Kepler’s launch in 2009 marked the beginning of some very exciting exoplanetary science which continues till date. The task at hand was again simple: to look at the brightness of a star over time and determine if there are any periodic dips in the brightness indicating the possible presence of an exoplanet around the star. The excitement I felt as a young teenager “analyzing” data from a telescope launched just a year before, possibly discovering new alien worlds was unparalleled. Participating in citizen science initiatives back then gave me a sense that I was doing something important for the scientific community even as a kid. 


Image 3: Example of Planet Hunters task
(Source: https://www.zooniverse.org/projects/nora-dot-eisner/planet-hunters-tess)

Citizen science has become an important facet of research in the scientific community today with it having evolved into more creative and interesting projects as new troves of data are generated. Citizen science projects can range from activities as simple as locating constellations with your naked eye monitoring light pollution (Globe at Night) to projects that involve amateur astronomers, photographers, and programmers equipped with certain level of hardware or skill to carry out the science. In this way, citizen science involves diverse groups from our society ranging from kids to amateurs to take part in various citizen science initiatives. For the younger section of the public, citizen science projects can become their introduction to scientific projects whereas it can be a leisure activity for the relatively senior members of our society. To me, citizen science initiatives are a powerful and effective tool for scientific outreach. Not only do members of the public learn about the science that is being carried out, they also actively contribute to it, developing a deeper interest over the years in such projects. Irrespective of the diversity in participation, one thing remains the same, all these groups contribute to our growing scientific knowledge about the world around us. 

But can the general public really contribute to the cutting-edge fields in science from their homes or backyards? Yes of course! Over the years, citizen science has churned out an interesting list of discoveries which have made it to scientific journals after being reviewed by scientists. One of the most notable discoveries in the field of space science which comes to mind is the discovery KIC 8462852 or more colloquially known as Boyajian’s star (named after Tabetha Boyajian, other names include Tabby’s star and WTF star). In 2015, citizen scientists who were part of Planet Hunters came across a star exhibiting odd levels of dimming (22%). Upon closer inspection by astronomers, the object’s odd behavior continued to baffle them leading to many people calling it by its nickname – the WTF star which is apparently a reference to the paper’s subtitle: “where’s the flux” (very misleading nickname, I know!). Scientists came up with various hypotheses to explain the star’s observed light curve which included possibilities of obstructions around the star occurring from a ring, planetary debris, or dust clouds. More farfetched hypotheses included the presence of large-scale artificial structures around the star being responsible for the unnatural dimming of the star’s brightness, hinting at the existence of intelligent civilizations. Scientists continue in their attempts to fully understand this bizarre star and hence Boyajian’s star is still being studied and monitored by subsequent telescopes and projects. 

I think most of us would agree science has changed a lot since ancient times. Science which started off as independent endeavors taken up by philosophers centuries ago today presents a different picture. The days of sitting under a tree and pondering on the mysteries of the universe and scribbling down equations are long gone. Most science carried out today is in large groups, relying on observed and measured data retrieved from instruments such as telescopes, particle accelerators, and robotic spacecraft. Hence, a huge amount of data is generated and will continue to be generated as next generation telescopes come into operation. Citizen science initiatives are a fantastic way of tackling this big data problem astronomy and space science is to expected to face soon. Thus, citizen science is not only valuable for outreach but also valuable in processing huge chunks of data and making meaningful contributions to the scientific community. A complete list of active and inactive citizen science projects in all scientific fields can be found at: https://en.wikipedia.org/wiki/List_of_citizen_science_projects

Read more at:
https://www.zooniverse.org/projects/zookeeper/galaxy-zoo
https://www.zooniverse.org/projects/nora-dot-eisner/planet-hunters-tess
https://www.darksky.org/globe-at-night-2021/
https://science.nasa.gov/get-involved/citizenscience/five-extraordinary-citizen-science-discoveries
Boyajian’s star discovery paper: Planet Hunters X. KIC 8462852 - Where's the Flux? Available at https://arxiv.org/abs/1509.03622

Sunday, May 1, 2022

I know what you did last summer: Grad School Edition

With May having just begun, undergraduate students are looking forward to the summer, but the situation is different for Professors and graduate students. Though few grad students take courses during this time of the year, it is nevertheless one of the busiest times of the year. Below, MSc student Justin Kerr explains why and describes some of the rhythms of graduate student life.

By Justin Kerr

“So, you are a student right? When does your summer break start?” It’s only April, and I’ve already been asked this question dreaded by graduate students everywhere three times. At least it’s not as bad as when I was on the hunt for an apartment! When you first become a grad student, you quickly realize that most people outside the realm of academia don’t understand what research based graduate school in the sciences entails. In reality, we are typically enrolled in few if any classes and most certainly do not get a multi-month vacation in the summer months. Course-based graduate programs do exist, but are much less common in the sciences and are typically excluded from receiving most of the normal funding. So, what do research-based grad students in physics actually do?

While grad students do take some courses, they typically make up the smallest portion of our time commitments throughout the degree. Here in the Physics and Astronomy program at York University, Master of Science students have the choice of pursuing a degree by thesis or a research project. In the case of a research project, students are required to take five one-semester courses throughout their two-year program. This type of degree is more common in physics programs for students looking to pursue a PhD at the same university in order to reduce course load during their PhD. It gives more variety in topics studied but allows less time for research. By the end of the degree, students are expected to have completed an original research project presented in the form of a large written document (although often somewhat shorter than a thesis). This type of degree is more common in some specific fields than others; for example, it is almost always used in particle physics, but is a rare choice in our own lab group. Personally, this is the option which I chose in order to expand my expertise in different areas of physics to support my future goals in academia. While this is the high course load option, it still means taking very few courses – the equivalent of a single semester in undergrad over two years, at least without compensating for enhanced difficulty of the material.

The thesis option instead requires only three courses be taken over the same two-year period. This allows students more time for research and development of a more intensive project. A thesis is typically longer than a research project and may involve more multiple smaller projects rather than the single one described in a master’s research project submission. Theses are also presented in a formal defense process instead of a simple submission to a supervisory committee. Completing a thesis gives a more complete research experience to students, which is more heavily valued in certain fields. In straight physics degrees, this can also be used as an option for students who are not intending on continuing in academia to provide a more complete education prior to moving to industry. Some universities other than York have very strict preferences for which type of degree is completed for moving forward in a PhD program, such as physics programs at the University of Toronto. When completing a PhD, the only option available is a thesis, and it will be much more intense than the MSc version. At York, a physics PhD requires the completion of six graduate courses, including any taken during the MSc – meaning a student who used the thesis option will take three courses throughout their four-year degree, and research project students will only need to take one. This means that thesis and PhD students are often not taking any courses at all in a given semester, and usually only one at a time if they are.

The main goal of a graduate degree in the sciences is to perform the research that will become the research project or thesis. To properly do this, we need to first perform literature searches and read many scientific papers pursuant to our planned project. We also keep up with relevant new research in our fields by reading new publications, with most graduate students often reading through several scientific publications per week. The bulk of our work is to perform our research tasks. In physics, this usually means coding, lab experiments, or some combination of the two. This is the portion of our responsibilities that means we don’t have a summer vacation! When other responsibilities do not get in the way, we are working on our research. Producing publications is also an important aspect of graduate education, which when combined with thesis requirements ensures that a good portion of our time is spent writing. We are generally expected to work roughly full-time hours (although deadlines often have something else to say about that!), with research and the associated writing taking up most of that.

The final portion of a graduate student’s responsibilities is teaching assistant duties. As part of our admission agreement and making up about half of our yearly funding are contracts to be teaching assistants for courses offered by our department or that of Natural Science, which covers science electives for non-majors. These can include grading assignments, teaching/demonstrating in a lab course, or leading tutorial sessions in undergraduate classes. The standard requirement for TAing is 270 hours per year, which usually averages out to about 10 hours per week during the Fall and Winter semesters while leaving the summer free to focus on research. In reality, much of that often ends up being concentrated into a few very busy weeks around midterm and exam grading time.

While a good portion of our funding comes from the relatively small portion of our work that is TAing, the truth is that the vast majority of our time spent on research is in fact still work. Since any of the few courses we do take usually occur during the Fall and Winter semesters along with our TAing, our summers are left free not for a summer vacation as it might for undergraduate students, but instead for a large focus on our research work. This is particularly important for those of us graduating in August such as myself who are likely to have some of the busiest months of our degrees ahead of us while we try to perfect our research projects and theses ahead of submission deadlines and defenses. The start of the summer is no better, with the start of May meaning research evaluations for all of us; these are where we must present our current work and future plans to our supervisory committee in a form of oral exam. The next time you are chatting with a grad student, make sure not to assume that they are looking forward to their nice summer vacation to take a break from the courses that they are likely not even taking!

Thursday, April 28, 2022

What Has the James Webb Space Telescope Been Up To?

PVL MSc student Madeline Walters has been following the launch and deployment of the James Webb Space Telescope with bated breath. This observatory will be a boon not only to the astronomical community, but also to the planetary science community. Above: the telescope's alignment evaluation image catches not only the target star, but myriad faint galaxies in the background.

by Madeline Walters

Since my last post about the James Webb Space Telescope (JWST), the telescope has reached its observing point and made some initial observations. The Webb is currently in orbit around L2, the second sun-Earth Lagrange point which is a gravitationally stable point about 1.5 million kilometers away from us. Since its launch, the spacecraft has gone through a few metamorphoses in preparation for its eventual observations. From testing a key antenna, to deploying its sunshield, each movement and maneuver has been integral to the telescope’s success. After successfully deploying the structure that binds the Webb’s two halves together, there was enough room to begin unfurling the massive sunshield that protects the telescope from harsh radiation. 

Soon after the sunshield was fully unfolded, the Webb deployed its two sunshield mid-booms, which stretched the sunshield out to its full length. This process requires the membranes to stretch to their proper tension, taking up to two days to tighten the sunshield. "As photons of sunlight hit the large sunshield surface, they will exert pressure on the sunshield, and if not properly balanced, this solar pressure would cause rotations of the observatory that must be accommodated by its reaction wheels," writes NASA public affairs specialist Alise Fisher in a blog post on December 30 after the launch. "The aft momentum flap will sail on the pressure of these photons, balancing the sunshield and keeping the observatory steady." It is a lot of very intricate and detailed steps that are necessary for every step of the operation-and for good reason. Every part of the unfolding must work in order to get the Webb to start observing. 

The next crucial part of the mission was the mirrors. On January 5, the telescope deployed its secondary mirror, unfolding a series of booms that hold the mirror out in front of the main mirror. This secondary mirror allows light to be collected and focused into a beam, which is then pushed down through the center of the telescope to a third mirror and other smaller ‘fine-steering’ mirrors which allow light to be properly allocated into the scientific instruments. 

Several days after the secondary mirror was deployed, the main mirror’s side panels were deployed, gearing up for the alignment of all 18 individual mirrors that make up the entire main mirror. And if you don’t think the word ‘mirror’ has been said enough so far - the observatory team spent about ten days working to move each mirror segment out of their preliminary launch alignments, and a lot longer for more precise alignment after that. However, for an instrument that will bring us observations for perhaps up to 20 years, a few months of alignment is worth it. 

Now at its destination for its science mission, the Webb has woken up, turned its instruments on, and has looked out into space to provide us with its first images. Its first telescope alignment evaluation image, made to only focus on the bright star in the center for alignment evaluation, shows background stars and galaxies due to the telescope’s optical sensitivity. Although there are still many months left before the JWST delivers its first full view of the cosmos, the telescope has already gone through an incredible journey made possible by an incredibly patient group of engineers and scientists.

Wednesday, April 13, 2022

How to tell time on Mars

This week, PhD Candidate Alex Innanen takes on a topic that has challenged planetary scientists and science fiction writers for decades: how do you tell time on a planet that has similarities in its revolutions to the Earth but some pesky differences? Often you'll hear of researchers working on Mars time because the length of its day is so similar to the Earth's. However, the match isn't perfect and can lead to unpleasant physiological effects for some and impractical, though hilarious, fixes. There is no 'Venus Time' or 'Jupiter Time' because their days are so different from ours that it makes no sense to try. But what to do with the extra 39 minutes in the martian day? Or the extra months needed in the martian year? 
(Image above from LMD's "Martian Seasons and Solar Longitude")

by Alex Innanen

One of my favourite things to read about are different calendars and methods of timekeeping. Here on Earth, there are all sorts of different calendars – the Gregorian, which you’re likely familiar with, the Julian calendar, and various lunar, solar or combination calendars. We also keep time within a single day in different ways – the standard now is a 24-hour clock, but at various times people have tried to introduce decimal time, where each day might have ten hours divided into 100 minutes. And this is just on our own planet, where generally the apparent movement of the sun and moon in the sky can give you a sense of when things are occurring.

Unsurprisingly, when you move to different planets things start to get more complicated.

Let’s take Mars for instance. Mars’ day (called a sol) is about 40 minutes longer than an earth day. If you want to use a 24 hour clock you either have to have a sneaky not-quite-an-hour-long 25th hour, or you have to make every hour a bit longer. Which is what the Mars clock that’s used for mission planning does. But wait, does that mean each hour has more than 60 minutes? Well, not really, if you make each minute a bit longer than an earth minute, and you can do that, not by adding extra seconds, but by making each ‘Mars second’ a bit longer than an Earth second. This way you can still use a familiar 24 hour clock.

This doesn’t mean that there’s some intrinsic ‘Martian second’ that is longer than an Earth second. While the second is an SI unit, it’s fairly arbitrary, as is splitting up a day into 24 hours. It’s just what we’re used to a second being.

One thing about round planets is that local noon – when the sun is directly overhead – happens at different times in different places. This is the reason that people on Earth invented time zones, so that local noon could line up – more or less – with noon on the clock. In reality, there’s a fair amount of variation even within a time zone. For example, there is about a 20 minute of difference between local noon in Toronto and Montreal just because of their difference in longitude, even though they use the same time zone.

There are no official time zones on Mars and missions tend to use local mean solar time (LMST), which is based on the average­ length of the sol, split into 24 hours. (There’s also local true solar time [LTST], which is referenced around the local noon, but drifts from 12:00 LMST throughout the year.) There is a generally accepted time standard for Mars, called Airy Mean Time (AMT) or Coordinated Mars Time (MTC) (comparable to Earth’s Greenwich Mean Time (GMT)/Coordinated Universal Time (UTC)) which refer to the mean solar time at Mars’ prime meridian, the crater Airy-1.

The other thing about Mars is its year is almost twice as long as an Earth year, about 668 sols or 687 Earth days. There is some familiarity, though, because Mars, like earth, has seasons! But Mars’ orbit is more eccentric than earth’s – that is to say, the path it travels around the sun is slightly more oblong. Earth also travels in an ellipse, and we do see the effects of not orbiting in a perfect circle on Earth seasons – the northern summer is about 94 days long, while the northern winter is only around 89 days – but not to so great an extent as on Mars. There the northern spring is 194 sols while the northern autumn is only 142 sols, a difference of 52 sols.

So what if we want to know what time of year it is? We can actually use the position of Mars (or any planet) in its orbit to tell this – specifically a parameter called solar longitude, shortened as Ls. We can start the year at a Ls of 0 degrees, the northern vernal equinox (the start of northern spring). Each subsequent season then starts at intervals of 90 degrees for a full 360 degree orbit. This convention is used in most scientific contexts because it can fairly easily tell you if events are occurring at around the same time year after year. It also avoids having to deal with things like leap years or leap seconds, because Mars’ orbit will always be 360 degrees – that’s just how geometry works.

All of this is what’s used currently to orient ourselves in time on Mars, but there have also been a number of attempts to create calendars and timekeeping systems that could be used by people living on Mars itself by everyone from scientists to fiction writers. The calendars divide the Martian year into months – which vary in their length, and in how many months there are in a year – and weeks – again, varying in length and quantity. Some calendars use familiar names for months and days of the week, and some make up new names, or new versions of the earth names. Getting into them all would probably take a whole series of blogposts, but it is a very fun rabbit hole to disappear down.

Wednesday, April 6, 2022

Lunar Cycles, Tides, and the Changing World

For those located near the coasts, it's impossible to miss the influence of planetary bodies (including the moon) upon the Earth. Twice a day, the sea level rises and falls. In some places, such as Canada's east coast Bay of Fundy, those changes can be quite dramatic. Here, liquid flowing on a spherical Earth, moving under a changing gravitational potential combines with the shallowness of the sea-floor to create a low-tide line kilometers from the high-tide line. As consistent as the system may seem, this "moon-driven [...] timeless circuit of invasion and retreat" may soon combine with longer-term effects of our changing climate, as PhD Candidate Giang Nguyen describes below.

By Giang Nguyen

Our lives are defined by astronomical cycles. How fast the Earth spins about its axis dictates our daily cycle. The angle between Earth’s spin axis with respect to its orbital plane tilts either the North Pole or South Pole towards the sun. How fast the tilt alternates between the North and the South directs our habits from season to season, year to year. These effects are the most apparent manifestations of astronomical forcing in our lives, but there are weaker forces at play that affect us in more subtle ways.
 
The Moon has its own cycles as well. The phases of the moon have often been used to keep track of time and many cultures use lunar calendars to this day. However, neither the Earth’s rotation nor the Moon’s orbit are in sync with the Earth’s orbit around the sun; we have to subtract and add days year to year to keep dates consistent with the seasons. The moon with its crescent shape is an important icon for many people across the world and indeed it does have its astronomical effect on us.
 
The moon’s gravity, along with the sun’s, exert tidal forces on Earth. These tidal forces shift water in our oceans from one place to another. You can imagine water sloshing back and forth in a bathtub and this is essentially what is happening in our ocean between the continental coasts. The movement of water will resemble standing waves where each node (point that experiences minimal amplitude change) is called an amphidromic point. Tidal forcing, along with the Coriolis effect, create huge hydrodynamical systems around these amphidromic points making them very important when trying to understand tides.
 
Seas that are somewhat enclosed by land such as the Gulf of Mexico and the Mediterranean Sea experience small tides. Regions that experience strong tides include northern Qu├ębec in Canada and France’s Bay of Biscay. These are the places where tides play a significant role in day to day lives, all resulting from how the moon orbits around Earth. Tidal effects are even strong enough to affect large climate systems [1].
 
The moon’s orbital plane around Earth does not line up with the Earth’s orbital plane around the sun. The wobble in the Moon’s orbit follows an 18.6 year cycle, called lunar standstills, and can translate to significant tidal effects. High-tide floods are already a reoccurring problem in many coastal regions. During periods in the cycle where tides are amplified, the risk of tide floods are predicted to be higher than ever. The next period of amplified tides is expected to arrive in the mid-2030s [2]. When this time comes, the Earth is predicted to be warmer and sea levels higher. Therefore, it is now more important than ever to continue to study the moon and tides and see how they affect the climate and weather around us.
 
Although our lives are mainly shaped around the sun, the moon still has its own special effects on Earth. The slight deviation in the moon’s declination as seen on Earth reveals a decade long oscillation that has significant implications on tidal forcing. This, in turn, may lead to climatic feedback that may redefine our everyday lives. Astronomical cycles remain a subject of great interest and I hope we get to learn more about it resultant from our relentless exploration of Space.

References:

[1] Lin, J., & Qian, T. (2019). Switch between el nino and la nina is caused by subsurface ocean waves likely driven by lunar tidal forcing. Scientific reports, 9(1), 1-10.

[2] Rasmussen, C. (2021). Study Projects a Surge in Coastal Flooding, Starting in 2030s. NASA JPL, https://www.nasa.gov/feature/jpl/study-projects-a-surge-in-coastal-flooding-starting-in-2030s

Tuesday, March 29, 2022

Exploring Active Planetary Defense & the DART Mission

One strong motivation for learning more about asteroids is to understand their potential for colliding with the earth. In this week's post, MSc student Ankita Das considers the Double-Asteroid Redirect Test, or DART, Mission. (Above: Asteroid Didymos and its moonlet Dimorphos taken by the Arecibo telescope is radar taken in 2003 Source: Arecibo Observatory/NASA)

by Ankita Das

With the launch of the Double Asteroid Redirection Test (DART) mission, the age of active planetary defense has formally begun. The DART mission is the first interplanetary spacecraft testing an asteroid redirection method to better prepare humankind for a potential mass extinction event due to the impact from a planetary body or asteroid fragment [1]. The spacecraft, launched in November 2021, is intended to crash into Dimorphos, a moonlet of asteroid Didymos, in September 2022, to see how much the speed and path of the moonlet can be altered.

Although this is the first dedicated spacecraft to be sent to an asteroid to study planetary defense techniques, ideas of such a mission have been around for decades.  In 1977, at NASA Ames Summer Study on Space Settlements, Dr. Brian O׳Leary, a former NASA astronaut candidate, proposed using mass drivers to move Earth-approaching Apollo and Amor asteroids to Earth’s vicinity during opportunities when the required velocity change to redirect them was low [2]. A critical development in this area occurred when a 2010 NASA study proposed the Asteroid Redirect Robotic Mission (ARRM) to use high-power solar electric propulsion technology to capture, and return an entire, very small (~10,000 kg), near Earth asteroid to the International Space Station [3]. In this article we reflect on how active planetary defense missions can safeguard us from a catastrophic impact events and if it is worthwhile to invest in a defense procedure.

The idea of protecting the planet from asteroid or cometary impacts emerged when researchers gained more knowledge about the small bodies of the solar system and investigated the impact history of the Earth. Upon investigation, scientists found multiple impacts from the Earth’s past, which have now been masked by erosion, geologic activities, and vegetation. The early discussions on planetary defense started once it was found that asteroid impacts most likely led to the mass extinction event that wiped out the dinosaurs. In the meantime, we also gained more knowledge about the small bodies of the solar system, informing scientists about the likelihood and frequency of potentially catastrophic impacts on the Earth. These studies also helped identify how past events from the Earth’s history could be linked to impacts from outer bodies [4].

For example, the infamous Tunguska event of 1908 involved an explosion equivalent 12 megatons of TNT, attributed to a meteor air burst, where a stony meteoroid of more than 50 m in diameter entered the Earth’s atmosphere at a speed of about 27 km/s and disintegrated near the Tunguska river in a sparsely populated region of Siberia in Russia. It was estimated that about 80 million trees over an area of 2150 sq. km. perished due to the impact [5]. More recently, an event that occurred in the city of Chelyabinsk, Russia in 2013 drew attention from the scientific community where a small asteroid - about the size of a six-story building - broke up over the city of Chelyabinsk. The asteroid, about 17 m in diameter and weighing approximately 10,000 metric tons, hit the Earth’s atmosphere at about 18 km/s. The energy of the resulting explosion exceeded 470 kilotons of TNT. The blast was so strong that it triggered detections from monitoring stations as far away as Antarctica [6].

Assessing Potential Threats

The Earth Impact Database [7], maintained by the University of New Brunswick, currently identifies as many as 190 confirmed impact structures on Earth’s surface. They range from small (tens to hundreds of meters in diameter) impact craters to large ones like Vredefort in South Africa measuring 160 km in diameter, dating back to 2023 million years. It is also true that not all impacts from outer bodies would result in terrestrial craters (i.e., they could explode in the atmosphere causing only air burst like the one at Tunguska), not all impact structures on the Earth’s surface have been identified [8]. Therefore, we may consider that these events are common and frequent on geologic timescales and the fact that our awareness of the population of potential impactors in the Solar System has been improving, how much of a threat do asteroids and comets really pose? 

Imagine the possibility of an asteroid with a diameter of more than 300 m heading towards a critical infrastructure like a nuclear plant. While the probabilities of such an event may be extremely low, it is essential that we develop our understanding of the risk associated with the entry of planetary bodies, considering the potential damage even a smaller asteroid (with diameter of less than 300 m) may cause to our civilization. Potentially hazardous asteroids and comets are categorized by NASA [9] and researchers [10]. The threat and potential of an impact primarily depend on the size and composition of the object, the surface being impacted, and the angle of impact. As of today, more than 28 000 near-Earth asteroids (NEAs) have been identified with majority of them having diameters in the range 30 – 100 m [11]. Smaller objects burn up in the atmosphere harmlessly as they approached the Earth. Larger objects, even if they burn up before hitting the ground, cause air burst or explosion, leading to severe damage.

To assess the potential damage and probability of impact, first, we need to detect these objects, and then we need to monitor their orbits. This is done from ground-based and space telescopes. By applying Newton’s laws and N-body simulations (i.e., modeling equations of motions for N objects interacting gravitationally), the orbits of most of these objects are predictable for at least 100 years into the future. Only the asteroids whose orbits cross that of the Earth are potentially dangerous. However, as mentioned earlier, not all asteroids are of the same size, and the larger the object, the higher is the threat. At the same time larger objects are rarer. Events like the Tunguska and Chelyabinsk were caused by smaller bodies compared to the events that caused the mass extinction approximately 66 million years ago due to an impact from as asteroid of diameter of about 10 km [12].

Thus, although the Solar System is populated with small bodies like asteroids and comets, only a fraction of these objects are of sizes that can be damaging and can potentially go on a trajectory that will coincide with the Earth to cause an impact. Asteroids that follow orbital trajectories within Earth's "neighborhood" (i.e., within 7.5 million km of Earth's orbit) around the Sun and that are more than 140 m in diameter are potential hazard to Earth and identified as Potential Hazardous Asteroids (PHAs) [13]. Ongoing research has enabled us to come up with a special classification of asteroids and objects which are closer to Earth’s orbit [14]. Not all near-Earth objects (NEOs) will impact the Earth at some point, but it is more likely that if an impact does happen, it will be an NEO.

Our Options for Defense

So, what are our options for defense as a species if an asteroid were to head our way? There are a few popular ideas. The first one is sending a spacecraft to the asteroid that can fragment the asteroid into smaller pieces. This idea sounds great but is not practical since the smaller fragments can also cause harm to the planet. Think of it as breaking down a big problem into 100 tiny chunks and having to deal with these 100 tiny chunks of the same problem. An alternate and favored line of action currently being investigated by the scientific community is deflecting the asteroid into a new orbit so that it misses the Earth completely. This can be achieved in a few ways. One would be to crash a spacecraft into the asteroid itself to gently nudge the asteroid into a newer orbit. This is what the DART mission is set to test on the asteroid Dimorphos, a small (160 m diameter) asteroid  in orbit around a larger orbit of the asteroid Didymos (780 m diameter). DART’s LICIACube spacecraft will crash on Dimorphos to create a kinetic impact that will change the orbit of Dimorphos around Didymos.

Image: Schematic of LICIACube attempting to change the orbit of Dimorphos
Image Source: Johns Hopkins Applied Physics Laboratory /NASA

Although Didymos is not a threat to Earth, this will be a demonstration of how effective the kinetic impactor method is when it comes to changing the course of an asteroid, called redirection.

Another idea involves the gravity tractor method that exploits the gravitational attraction of a spacecraft with the asteroid to cause continuous minuscule changes in the orbit, which would, cumulatively, over time result in a more visible change of the trajectory of the asteroid. The only downside to this method is it is a long process that involve several years [15], and hence we will need to know about the asteroid well in advance from the date of potential impact. This brings us to the question, what happens if we discover an asteroid heading our way and we do not have sufficient time to send a spacecraft to the asteroid to deflect it? Such a scenario will call for a damage control strategy where the trajectory of the asteroid is monitored, the potential places on the Earth where the asteroid is expected to impact is calculated, and measures are taken to minimize the damage that could be caused to life or infrastructure.

To conclude, planetary defense is an exciting field of study which is necessary for the safekeeping of the planet. In 2016 NASA established the Planetary Defense Coordination Office (PDCO) to manage its ongoing mission of planetary defense. NEOs and NEAs need to be monitored constantly, in addition to the continued identification and discovery of additional potential impactors capable of significant damage so that we can prepare for a potentially catastrophic impact event. The DART mission is a critical mission that will be our first step in equipping ourselves better in the event of a hazardous asteroid coming Earth’s way.

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Sources:

[1]  https://www.nasa.gov/specials/pdco/index.html 
[2] Mazanek, D. D., Merrill, R. G., Brophy, J. R., & Mueller, R. P. (2015). Asteroid redirect mission concept: a bold approach for utilizing space resources. Acta Astronautica, 117, 163-171.
[3] https://authors.library.caltech.edu/86061/1/Asteroid_Redirect_Robotic_Mission.pdf
[4]  Sleep, N. H., Zahnle, K. J., Kasting, J. F., & Morowitz, H. J. (1989). Annihilation of ecosystems by large asteroid impacts on the early Earth. Nature, 342(6246), 139-142.
[5] https://www.sciencedirect.com/science/article/abs/pii/S0019103518305104?via%3Dihub
[6]  https://www.space.com/33623-chelyabinsk-meteor-wake-up-call-for-earth.html
[7]  http://www.passc.net/EarthImpactDatabase/New%20website_05-2018/World.html
[8]  https://www.boulder.swri.edu/~cchapman/crcepsl.pdf
[9]  https://cneos.jpl.nasa.gov/about/neo_groups.html
[10]  http://www.boundarycondition.com/NEOwp_Chapman-Durda-Gold.pdf
[11]  https://cneos.jpl.nasa.gov/stats/size.html
[12]  https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JE01743
[13]  https://solarstory.net/asteroids/near-earth-asteroids
[14]  https://space.nss.org/national-space-society-planetary-defense-library/
[15]  https://iaaspace.org/wp-content/uploads/iaa/Scientific%20Activity/conf/pdc2015/IAA-PDC-15-04-11.pdf 

Monday, March 14, 2022

Water Discovered on Mars! (Again.)

It's a bit of a running joke amongst planetary scientists that any research discussing water (in any form) on Mars will get reported in the press with a breathless headline. Year after year, somehow the 'discovery' of water on Mars persists as a topic of great interest. One of our MSc students digs into this phenomenon below. Luckily, she isn't working on astrobiology topics - that often leads to headlines about aliens.
(Image above: Jezero crater, as it might have appeared when filled with water in the past)

By Grace Bischof

Recently, fellow PVL member Charissa Campbell was involved in a JPL press release detailing the Martian clouds she captured in her Cloud Altitude Observation. The images consisted of beautiful clouds drifting across the Martian sky, likely composed of CO2-ice due to their high altitude in the atmosphere. I spent some time reading the replies to the press release on social media, many of which pose questions about the composition of the clouds on Mars. “Clouds means water?” writes one of the commenters. Meanwhile, “What are the clouds made of? [because] there ain’t no water vapour floating around on Mars, right?” inquires another.  

Well, I have some good news for everyone: there is water on Mars! But before you call your local newspaper to report the exciting revelation, I have some explaining to do. The presence of water on Mars has been confirmed since the late 1960s, when water vapour lines were detected in spectra of Mars observed with an Earth-based telescope. Since then, water has been “discovered” on Mars over and over and over again (see: any Daily Mail article about Martian water). So, let’s clear this up. Water exists on Mars in both vapour and ice form. The confusion arises when we consider the way we talk about water in day-to-day life. In regular conversation, we say “water” when we mean liquid H2O, and “ice” when we mean solid H2O. This verbiage doesn’t hold in planetary science settings because “ice” to refers to any solid form of a condensable species: for example, CO2-ice or H2O-ice. Because of this confusion, the lack of liquid water leaves people believing there is no water whatsoever.

So, let’s take a closer look at the water on Mars. Mars’ atmosphere is much thinner and has much less water vapour than Earth’s atmosphere. However, the amount of water vapour is sufficient to condense to form water-ice clouds in the atmosphere. Each Mars Year, when the planet is at its aphelion position (the furthest point from the sun) a belt of water-ice clouds forms in the equatorial region of the planet, called the Aphelion Cloud Belt. These clouds have been observed by orbiters around Mars and cameras on the surface, notably by the Curiosity rover. Water-ice clouds exist in other regions, as well, such as in the Martian Arctic. The Phoenix mission captures images of fluffy clouds drifting past its landing site during the second half of the mission. The Surface Stereo Imager and lidar onboard the lander were used together to find evidence of water-ice fog near the surface of the lander. The Phoenix mission was also the first mission to capture precipitation (snow) falling from the clouds.

The other common place to find water on Mars is as water-ice in the subsurface. The Phoenix lander was equipped with a robotic arm to dig into the Martian soil. They were able to find ice in the area around the lander at many depths, ranging down to 14 cm. At both the north and south poles you can find a large polar cap primarily composed of water-ice covered by a layer of CO2-ice. Areas of the south polar cap resemble Swiss Cheese, where pits in the CO2-ice layer expose water-ice beneath. PVL member, Alex Innanen, has examined the Swiss Cheese pits to determine if the water vapour sublimated from the Swiss Cheese contributes substantially to the overall global water vapour abundance. 

So, what about that coveted liquid water? Well, it’s complicated. Presently, no bodies of liquid water can exist on the surface of Mars. The atmosphere is so thin that exposed water-ice sublimates straight to water vapour when heated and deposits back to ice when cooled. Geomorphic evidence, such as river deltas, show us that Mars had liquid water on the surface in its past. In 2018, radar analysis of Mars’ south pole saw evidence of a subsurface liquid-water lake. It was theorized the lakes would be extremely salty, bringing the freezing temperature down and allowing the water to stay liquid. In 2021, a York U professor, Dr. Isaac Smith, released a paper explaining that the radar observations are better described by hydrated and cold clay-rich deposits (https://doi.org/10.1029/2021GL093618), rather than salty lakes. 

Liquid water on Mars is an exciting notion because it leads to many questions about the habitability of the planet, both past and present. But liquid water is not the only interesting phase of water – it is clear we really love the clouds here at PVL. Nonetheless, if liquid water is ever found, you can sure expect to see a bold headline declaring “Water Discovered on Mars!”, in which case, you can refer back to this blog post.