It's meteor shower season once again - but what actually are they?

Anyone who has spent time lying back and casually looking up at the sky has likely seen the fiery trail of a meteor which streak across the sky every few minutes on a typical night. During meteor showers, the rate can increase dramatically and all of the meteors appear to originate near a point called the radiant. This week Justin Kerr discusses the source of these fascinating features of the night sky.

(Image source: NASA/Bill Dunford)

by Justin Kerr

With another year of the Perseid meteor shower drawing to a close next week, many of us have been lucky enough to see quite the show while outside of the city. For those who haven’t, you still have until approximately August 24th to catch a glimpse of it – and if you can’t get a good view by then, there will be more opportunities to see a major meteor shower later in the fall. But what actually are these meteor showers, and why is it that each one appears at the same time each year like clockwork?

Meteor showers are events in which a large quantity of meteors are visible in the sky and all appear to be originating from a single point in the sky. This apparent singular origin is how each of the recurring showers derives it’s name, with the shower taking on a name based upon the constellation which contains that apparent origin of the meteors. The meteors themselves are caused when small pieces of rock (meteoroids) enter the Earth’s atmosphere while traveling at tens of thousands of km/h (tens of km/s) relative to the Earth and begin to burn up. Since the rocks involved in meteor showers are typically only around the size of sand grains, they completely burn up in the atmosphere and never impact the Earth as a meteorite. Even though they are so small, we can still see such bright light as they burn up thanks to the intense heating by friction with the air resulting from their high velocities. Some meteors even leave trails of ionized gases in their wake, giving us a glowing trail to see for a few seconds after the meteor has burned up. The reason they all originate from the same apparent location along with why they occur on a yearly schedule is linked to the origin of these small space rocks.

These large groups of meteoroids striking the Earth are not just bits of rock leftover from the birth of the solar system or visitors from the asteroid belt. They stay in very specific orbits, which gives astronomers a clear clue to their origin. The meteors we see during meteor showers are in fact the remains of comets, which fill their orbit with debris as the ice holding them together melts away each time they pass the sun until eventually they are all that is left. Due to conservation of momentum, the small rocks contained in the comets stay in the same orbit as the comet once breaking free. At this point, we then have an orbit filled with meteoroids ready for Earth to strike instead of one large comet.

The yearly recurrence of meteor showers is simply due to the astronomical definition of the year itself – the (approximate) time it takes for the Earth to complete a full revolution around the Sun. The orbit of the Earth crosses the orbit of each dead or dying comet only at one point. Every time the Earth reaches that point in the orbit each year, it swings through the cloud of meteoroids and gives us a beautiful show in the night sky. Each of the different meteor showers we are familiar with come from the remains of a different comet, and so occur at a different time of the year when the Earth reaches that intersection location in it’s orbit around the Sun. The currently occurring Perseid meteor shower comes from the comet Swift-Tuttle, while the upcoming Orionids are leftovers from the famous Halley’s Comet. There are two meteor showers which are thought to be caused by the remains of asteroids instead of comets, most notably the Geminids originating from 3200 Phaethon, but all others we know of are the result of comets.

While many of us may fear the impact of a whole comet or asteroid, the tiny pieces of them hitting us during meteor showers are an entirely different story. To see for yourself, keep an eye on the sky during the night up until August 24th to catch the Perseids. The best time for viewing meteor showers is typically just before dawn, but any time after dark when the constellation the shower is named after is visible will do. While you will have a much better chance of seeing a meteor if you are outside of the city, it is even possible to catch some here in Toronto – I have even been lucky enough to spot a few while taking my dog for a walk in the cooler weather after dark! For a much better show, you can check out various areas outside of the city with a much darker sky – for areas relatively near Toronto, I can suggest the Torrance Barrens Dark Sky Preserve or a camping trip to Long Point Provincial Park (pandemic restrictions permitting). While the Perseids are nearly finished for the year, some of the other best opportunities for viewing a meteor shower this year are yet to come with the Orionids peaking on the night of October 21st, the Leonids on Novermber 16th, and the Geminids on December 13th. Make sure to keep your eyes on the sky this fall and catch a glimpse of the fiery end of some tiny pieces of comet! 

Head in the Martian Clouds: a Research Update

 

As Conor mentioned a few posts ago, just because a mission ended in the past doesn't mean that all the useful science from that mission has been extracted. This week, Grace tells us about some research she has been completing applying new models to old data in order to make new discoveries. I have a particular affinity for this kind of science. Truly, it justifies the investment made to keep a record of all data returned from other planets and to make that data available to anyone with a theory to test. In a way, it reminds me of the curation of returned samples, only a fraction of which are consumed by the planned laboratory testing once they are returned to Earth. A portion of each sample is held back, waiting for future questions, theories and experimental techniques to be invented that will unlock mysteries unknown to present-day planetary science. The Image above of the Phoenix Lander at Green Valley, Mars is credited to Corby Waste (NASA/JPL). This image was created prior to landing and therefore is missing the periglacial features that were seen at the actual landing site. It's based off a famous image from a previous rover.

 

By Grace Bischof 

Over the past couple of weeks, I have been wracking my brain to come up with a good topic to write about for my round of the blog post. I realized I am now just shy of my first-year anniversary as a PVL member (where did the time go!?). With a little experience under my belt, I figured it would be a good time to finally give an update on the research I’ve been doing over the last year – and especially the past 8 months. Since I had no classes to worry about, I could dedicate the majority of my working hours to my project. 

The project I’ve been working on was originally assigned to me with a need for a project to work on from home. My initial project – MAGE – which I briefly talked about in my introductory blog post last year, is all lab-based. Obviously, with multiple lock-downs and very limited access to campus, I have not been able to work on MAGE. Thus, the Phoenix project was born. 

To start, the Martian atmosphere is very thin, and has a weak greenhouse effect compared to Earth. The daily temperature on Mars is essentially mediated by visible-band radiation coming in from the sun, where it is absorbed by the surface, then re-radiated back into space as thermal radiation. Aerosols in the atmosphere – in the form of dust or water-ice particles – can produce a secondary effect on the temperature. Water-ice particles scatter a portion of the incoming solar flux and, importantly to this project, absorb and reflect outgoing longwave flux. This increases the thermal radiation at the surface, which can increase warming.

This work is dubbed “the Phoenix project” because it is based on the Phoenix mission, which landed on Mars in 2008. The Phoenix lander was, and still is, the most northern-based lander on Mars, where it was equipped with instruments to study the local meteorology and water cycle in the Martian polar region. Phoenix operated for 150 sols, beginning at the end of northern Spring, and carrying through summer solstice into the mid-summer. During its mission, Phoenix made many detections of water-ice clouds, fog, and made the first observation of water-ice precipitation on Mars.

So, how does this all relate? Well, while the LIDAR and camera onboard the lander captured important information about the clouds near Phoenix, these instruments could only operate for a small fraction of the entire mission length. On the other hand, the temperature sensors on the lander made near-continuous observations for the entire mission, measuring the atmospheric temperature every 2 seconds. Since we know that clouds can have an effect on the temperature, by modelling the atmospheric temperature at the Phoenix site, we can create a full record of the cloud activity.

Building the cloud record involves using a surface energy balance at the location of the lander. This includes all energy flux components that will influence the temperature, such as radiative effects of dust in the atmosphere. The energy balance contains one parameter, R, which is solely attributed to the flux reflected by water-ice clouds. The ground temperature is modelled using a subsurface conduction scheme involving various regolith properties, and the atmospheric temperature is found by an equation involving the ground temperature and the sensible heat flux. R is then determined by comparing the modeled air temperature to the air temperature collected by the temperature sensor aboard Phoenix. If the temperatures are a perfect match, R = 0 over the entire run, and it is assumed no clouds are present. Otherwise, the temperatures are matched by varying R on 2-hour intervals within the model. 

Completing this analysis for every sol of the mission builds up a continuous picture of the reflected flux throughout the mission. The reflected flux can be related to cloud properties such as optical depth and ice-particle radius. This is the portion of the project I am currently working on. I believe this project has helped strengthen my research skills, as the methods went through several iterations in the beginning and we had to work through many problems that were occurring. While this isn’t the project I was given initially, I have really enjoyed the time I’ve spent working on the Phoenix project and my enthusiasm for Martian meteorology has really grown.

Pizza in the Park – The Socially Distant Version

 Each year, I* host two social gatherings for PVL that set aside work and science and allow us all to interact with one another in a more informal context. The summer version has come to be known as "Dr. John's Pizza Party in the Park" due to the many excellent pizza places located in Toronto. The 2020 edition was held virtually, but in 2021 we decided to go with a socially distanced in-person event. Rents being what they are in Toronto and with everyone working from home, the group is spread across a large geographic region. As a result, we elected to move this year's event to a more central location for the group - Rouge Beach in Scarborough. Here's a water-side photo from the event.
(*in case you didn't know, dear reader, all these short intros to the PVL articles are written by the lab director)

by Charissa Campbell

A few weeks ago, our research group decided to take a big step and have an outdoor socially distant gathering. In some cases, some members of our group have never met each other in person, seen campus or even know the height of our supervisor. The pandemic has changed so much in our daily lives, but now with basically all of us fully vaccinated, we figured it was a good first step to finally meet each other in person.

We decided to go to Rouge National Urban Park, which is a rather large park but has a great section right on the lake with lots of trails, views and even a boardwalk through a swampy area. The area we were specifically interested in was Rouge Beach, right on the lake. One convenience about this part of the park is the nearby GO train station that connects to multiple cities. They are double decker trains traveling between Toronto (Union) and Oshawa on that particular line. It definitely makes visiting that park ideal because of the ability to access it directly off the train. 

Trains have always been an interest of mine and I have many memories of watching the trains go by wondering if there was a caboose or not at the end. A caboose was placed at the end of the train and were a manned railway car. The crew were able to monitor the train from the back and apply emergency brakes if necessary. However, with the rise of technology an alternative was created called the end-of-train device that is a suitcase-sized box that attaches to the last car. It relays air-brake pressure measurements and the velocity at the end of the train, all to the engineer at the front (https://www.chicagotribune.com/news/ct-xpm-1995-02-02-9502020309-story.html). This smaller, more portable version eventually replaced the caboose and in 1989 the first cabooseless train made its first trip between Winnipeg and Thunder Bay (https://www.cbc.ca/archives/entry/1989-railways-reduce-caboose-use). By the time I was a kid watching the trains go by, a caboose was rather rare but occasionally you’d see one which was worth the wait. Unfortunately, the Go trains do not have a caboose, but the double decker feature makes for great views of the lake.

A caboose on display at the Toronto Railway Historical Association

Once we all arrived at the park, we spent some time at some conveniently placed rocks. They were right on the water and was a great spot to get an updated lab photo. Several people have left the group since our last big group adventure, such as PDFs Christina Smith and Paul Godin, but we’ve also gained several valuable members to our team (Haley, Grace, Conor, Justin). Over time our group will change here and there as people graduate and, hopefully, we will be able to keep up with lab photos to see more of the progression from year to year.

Next, we moved to a grassier area that allowed us to sit in a good socially distant manner. We engaged in frisbee and volleyball and simply took the time to get to know each other. Pizza is the typical food we eat for group outings, so we shared some pizza, sat on the grass and chatted about whatever came on our mind. It was really great to be back in a situation where you can see people face to face. To do this, it is very important to go get your vaccine so you too can start making the progression back to the life we used to remember.

It’s been quite some time since life was all maskless events. I have a picture frame in my office that still says “coming soon…” for my son, Arthur, and yet he just turned 14 months. Now that I have been fully vaccinated, I have applied for lab access so I can slowly start returning to my office and start working on a big lab-based project I am leading. The only way this is possible is to get vaccinated so that not only you can be protected, but so that it doesn’t spread to children who cannot get a vaccine yet. This is still a concern of mine as unfortunately my son won’t be able to get the vaccine for a while still. Therefore, there is still a chance he could still catch covid, unless more people get vaccinated. Things may not go back to what we remember them to be, but I know myself and my family will be better off now that we’ve got our vaccines.