Al Stahler: Two stories — Mars and the virus
Let’s take a walk in the garden. So as not to get lost, we’ll take a map. We’ll start in the pumpkin patch, and put a dot on the map to show where we are.
We visit the carrot crop, take a break on the broccoli bench, head on to the spinach spot. At every stop, we put another dot on the map.
At the end of our journey, we can connect the dots, and trace our path.
We can do the same with a map of the sky, to trace the paths of the planets, as they move among the stars, one night to the next.
Astronomers have been making such maps of the sky for thousands of years. And they asked, “What would this map look like if we were watching the planets move, not from Earth, but from another viewpoint, looking down on the sun, on the planets, on Earth?”
Not-so-many hundreds of years ago, they came to realize that the planets do not circle Earth, as had been taught. Rather, all the planets – including Earth – circle the sun.
Though we say that Earth and planets “circle” the sun, their orbits are not true circles. Planetary orbits are elliptical – they’re “squashed circles” – which puts each planet sometimes closer to the sun, sometimes farther away.
Last Saturday afternoon – 4:34 p.m. – Earth reached its farthest point from the sun. Though we learn in school that Earth lies 93 million miles from the sun, that’s just an average. Last Saturday – and still today – Earth was a good ninety-four-and-a-half million miles out from the sun. Earth is closest to the sun, not in summer, but in winter … which, with various wobbles, conspires to throw our planet into, then pull us out of, an ice age. More about that in another column.
Every planet is closer to the sun at some point in its orbit, farther from the sun at another.
Allow me to suggest you head outside before dawn, either Friday or Saturday. If you have a good view to the east, you’ll see planet Venus, shining bright as the morning star. Much higher in the sky will be the roughly third-quarter moon. And, close to the moon, will be the ruddy planet Mars – the next planet out from the sun, after Earth.
Moving along its elliptical orbit, Mars will be closest to the sun next month. With Earth at its farthest point from the sun, and Mars approaching its closest point, Earth and Mars are approaching each other.
If you want to send a robot geologist to study the rocks of Mars – to see what Mars was like, billions of years ago, when life was just starting out on Earth — to see whether life might also have then been starting out on Mars — the best time to launch would be when the two planets are close.
I was visiting southern California, something over a year ago, to see such a robot geologist being assembled at JPL – NASA’s Jet Propulsion Lab. We can only launch such a mission when Earth and Mars are close – once every two-plus years. So if we want to get our robot geologist to Mars, we’ve got to get it off Earth, and into space, before the middle of August.
The robot geologist Percy – formal name, Perseverance – could have launched around the middle of next week … but stuff happens. One bug after another has cropped up in the launch system, so that the earliest launch date is now the end of this month. From the end of July to the middle of August gives Percy just two weeks to get off the ground, or be forced to wait – as the European Space Agency’s rover is being forced to wait – another two-plus years, until 2022.
Many people infected with SARS-CoV-2 – the virus that causes COVID-19 – suffer mild, even no symptoms. Some, though, suffer badly; some find it hard to breathe.
If we feel cold, we turn up the thermostat. The furnace ignites, and the room grows warmer. When the temperature reaches its set-point, the thermostat signals the furnace to shut down. The thermostat gives the furnace feedback, as to how it’s doing its job. The signal to shut down – to stop what it’s doing – is negative feedback.
An insect bites. Your flesh swells up … turns red … grows warm … becomes inflamed. Scrape your arm; spend too much time in the sun; accidentally inject some nasty bacteria beneath your skin, where they grow into an infection. Once again, your flesh becomes inflamed.
Inflammation is a general response of our bodies to injury or infection. Damaged or infected cells shout out for help, asking the body to fight the infection; to repair the damage; to clean up the mess.
The body responds with messages of its own, triggering the region to become inflamed – to turn up the thermostat. These messages are carried by hormones called cytokines.
Cytokines trigger blood vessels to carry more blood to the region, causing the tissue to swell and turn red; blood vessels become leaky, allowing white blood cells (WBCs) to deploy to fight the infection, and to remove the detritus, broken bits and pieces of cells. Damaged cells are repaired or replaced.
As the infection is quashed, the damage repaired, the mess cleaned up, signals go out to turn off the inflammation response – the body receives negative feedback, telling it to stop sending out cytokines.
That’s what’s supposed to happen.
The singer’s voice goes into her microphone; the mic sends the sound to the amplifier, which boosts the sound, then sends it to the speakers.
Suppose the singer gets too close to the speakers. Her mic picks up the already-loud sound, and sends it to the amp, which boosts it yet more and sends it, once more, to the speakers … from where it again enters the mic, the amp, the speakers. ‘Round and ‘round, louder and louder, the music becomes a piercing squeal: Positive feedback.
I asked Stanley Perlman (University of Iowa), who studies corona viruses (SARS, MERS, and now SARS-CoV-2, which causes COVID-19), why SARS-CoV-2 is so damn infectious. SARS and MERS, it turns out, do not infect the upper respiratory tract, and have to get lucky to get into the lungs. But SARS-CoV-2 does infect the upper respiratory tract; from there, it’s an easy jump to the lungs.
Once an infection is quashed, the damage repaired, the mess cleaned up, negative feedback is supposed to shut down the inflammation. But sometimes – for reasons mysterious – cytokines continue to be produced. Inflammation grows, out-of-control, making breathing difficult … too difficult, it leads to death, from a “cytokine storm.”
Al Stahler enjoys sharing science and nature with friends and neighbors on KVMR-FM, and can be reached at firstname.lastname@example.org.
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