The human mind may find it difficult to conceptualize: a cosmic cloud so colossal it surrounds the Sun and eight planets as it extends trillions of miles into deep space.

The spherical shell known as the Oort Cloud is, for all practical purposes, invisible. Its constituent particles are spread so thinly, and so far from the light of any star, including the Sun, that astronomers simply cannot see the cloud, even though it envelops us like a blanket.

It is also theoretical. Astronomers infer the Oort Cloud is there because it’s the only logical explanation for the arrival of a certain class of comets that sporadically visit our solar system. The cloud, it turns out, is basically a gigantic reservoir that may hold billions of icy celestial bodies.

Two of those bodies will pass by Earth in the days leading up to Halloween. Tsuchinshan-ATLAS, also known as Comet C/2023 A3, will be at its brightest, and likely visible to the naked eye, for a week or two after Oct. 12, the day it’s closest to Earth – just look to the western sky shortly after sunset. As the days pass, the comet will get fainter and move to a higher part of the sky.

The second comet, C/2024 S1 (ATLAS), just discovered on Sept. 27, should be visible around the end of October. The comet will pass closest to Earth on Oct. 24 – look low in the eastern sky just before sunrise. Then, after swinging around the Sun, the comet may reappear in the western night sky right around Halloween. It’s possible, however, that it could disintegrate, in part or in whole, as sometimes happens when comets pass by the Sun – and this one will come within 1 million miles (1.6 million kilometers) of our star.

As a planetary astronomer, I’m particularly curious about the Oort Cloud and the icy bodies inhabiting it. The Cloud’s residents may be a reason why life ignited on Earth; crashing on our planet eons ago, these ice bodies may have supplied at least some of the water that all life requires. At the same time, these same objects pose an ever-present threat to Earth’s continuation – and our survival.

Billions of comets

If an Oort Cloud object finds its way to the inner solar system, its ices vaporize. That process produces a tail of debris that becomes visible as a comet.

Some of these bodies, known as long-period comets, have orbits of hundreds, thousands or even millions of years, like Tsuchinshan-ATLAS. This is unlike the so-called short-period comets, which do not visit the Oort Cloud and have comparatively quick orbits. Halley’s comet, which cuts a path through the solar system and orbits the Sun every 76 years or so, is one of them.

The 20th-century Dutch astronomer Jan Oort, intrigued by the long-period comets, wrote a paper on them in 1950. He noted about 20 of the comets had an average distance from the Sun that was more than 10,000 astronomical units. This was astounding; just one AU is the distance of the Earth from the Sun, which is about 93 million miles. Multiply 93 million by 10,000, and you’ll find these comets come from over a trillion miles away. What’s more, Oort suggested, they were not necessarily the cloud’s outermost objects.

Nearly 75 years after Oort’s paper, astronomers still can’t directly image this part of space. But they do estimate the Oort Cloud spans up to 10 trillion miles from the Sun, which is almost halfway to Proxima Centauri, the next closest star.

The long-period comets spend most of their time at those vast distances, making only brief and rapid visits close to the Sun as they come in from all directions. Oort speculated the cloud contained 100 billion of these icy objects. That may be as numerous as the number of stars in our galaxy.

How did they get there? Oort suggested, and modern simulations have confirmed, that these icy bodies could have initially formed near Jupiter, the solar system’s largest planet. Perhaps these objects had their orbits around the Sun disturbed by Jupiter – similar to how NASA spacecraft bound for destinations from Saturn to Pluto have typically swung by the giant planet to accelerate their journeys outward.

Some of these objects would have escaped the solar system permanently, becoming interstellar objects. But others would have ended up with orbits like those of the long-period comets.

Threats to Earth

Long-period comets present a particular potential danger to Earth. Because they are so far from our Sun, their orbits are readily altered by the gravity of other stars. That means scientists have no idea when or where one will appear, until it does, suddenly. By then, it’s typically closer than Jupiter and moving rapidly, at tens of thousands of miles per hour. Indeed, the fictional comet that doomed Earth in the film “Don’t Look Up” came from the Oort Cloud.

New Oort Cloud comets are discovered all the time, a dozen or so per year in recent years. The odds of any of them colliding with Earth are extremely low. But it is possible. The recent success of NASA’s DART mission, which altered the orbit of a small asteroid, demonstrates one plausible approach to fending off these small bodies. But that mission was developed after years of studying its target. A comet from the Oort Cloud may not offer that much time – maybe just months, weeks or even days.

Or no time at all. ‘Oumuamua, the odd little object that visited our solar system in 2017, was discovered not before but after its closest approach to Earth. Although ‘Oumuamua is an interstellar object, and not from the Oort Cloud, the proposition still applies; one of these objects could sneak up on us, and the Earth would be defenseless.

One way to prepare for these objects is to better understand their basic properties, including their size and composition. Toward this end, my colleagues and I work to characterize new long-period comets. The largest known one, Bernardinelli–Bernstein, discovered just three years ago, is roughly 75 miles (120 kilometers) across. Most known comets are much smaller, from one to a few miles, and some smaller ones are too faint for us to see. But newer telescopes are helping. In particular, the Rubin Observatory’s decade-long Legacy Survey of Space and Time, starting up in 2025, may double the list of known Oort Cloud comets, which now stands at about 4,500.

The unpredictability of these objects makes them a challenging target for spacecraft, but the European Space Agency is preparing a mission to do just that: Comet Interceptor. With a launch planned for 2029, the probe will park in space until a suitable target from the Oort Cloud appears. Studying one of these ancient and pristine objects could offer scientists clues about the origins of the solar system.

As for the comets now in Earth’s vicinity, it’s OK to look up. Unlike the comet in the DiCaprio movie, these two will not crash into the Earth. The nearest Tsuchinshan-ATLAS will get to us is about 44 million miles (70 million kilometers); C/2024 S1 (ATLAS), about 80 million miles (130 million kilometers). Sounds like a long way, but in space, that’s a near miss.

Uncommon Courses is an occasional series from The Conversation U.S. highlighting unconventional approaches to teaching.

Title of Course

Evidence-Based Happiness for Teachers

What prompted the idea for the course?

I was discouraged. For nearly three decades, as a clinical psychologist, I trained mental health professionals on suicide assessment. The work was good but difficult.

All the while, I watched in dismay as U.S. suicide rates relentlessly increased for 20 consecutive years, from 1999 to 2018, followed by a slight dip during the COVID-19 pandemic, and then a rise in 2021 and 2022 – this despite more local, state and national suicide prevention programming than ever.

I consulted my wife, Rita, who also happens to be my favorite clinical psychologist. We decided to explore the science of happiness. Together, we established the Montana Happiness Project and began offering evidence-based happiness workshops to complement our suicide prevention work.

In 2021, the Arthur M. Blank Family Foundation, through the University of Montana, awarded us a US$150,000 grant to support the state’s K-12 public school teachers, counselors and staff. We’re using the funds to offer these educators low-cost, online graduate courses on happiness. In spring 2023, the foundation awarded us another $150,000 so we could extend the program through December 2025.

What does the course explore?

Using the word “happiness” can be off-putting. Sometimes, people associate happiness with recommendations to just smile, cheer up and suppress negative emotions – which can lead to toxic positivity.

As mental health professionals, my wife and I reject that definition. Instead, we embrace Aristotle’s concept of “eudaimonic happiness”: the daily pursuit of meaning, mutually supportive relationships and becoming the best possible version of yourself.

The heart of the course is an academic, personal and experiential exploration of evidence-based positive psychology interventions. These are intentional practices that can improve mood, optimism, relationships and physical wellness and offer a sense of purpose. Examples include gratitude, acts of kindness, savoring, mindfulness, mood music, practicing forgiveness and journaling about your best possible future self.

Students are required to implement at least 10 of 14 positive psychology interventions, and then to talk and write about their experiences on implementing them.

Why is this course relevant now?

Teachers are more distressed than ever before. They’re anxious, depressed and discouraged in ways that adversely affect their ability to teach effectively, which is one reason why so many of them leave the profession after a short period of time. It’s not just the low pay – educators need support, appreciation and coping tools; they also need to know they’re not alone.

What’s a critical lesson from the course?

The lesson on sleep is especially powerful for educators. A review of 33 studies from 15 countries reported that 36% to 61% of K-12 teachers suffered from insomnia. Although the rates varied across studies, sleep problems were generally worse when teachers were exposed to classroom violence, had low job satisfaction and were experiencing depressive symptoms.

The sleep lesson includes, along with sleep hygiene strategies, a happiness practice and insomnia intervention called Three Good Things, developed by the renowned positive psychologist Martin Seligman.

I describe the technique, in Seligman’s words: “Write down, for one week, before you go to sleep, three things that went well for you during the day, and then reflect on why they went well.”

Next, I make light of the concept: “I’ve always thought Three Good Things was hokey, simplistic and silly.” I show a video of Seligman saying, “I don’t need to recommend beyond a week, typically … because when you do this, you find you like it so much, most people just keep doing it.” At that point, I roll my eyes and say, “Maybe.”

Then I share that I often awakened for years at 4 a.m. with terribly dark thoughts. Then – funny thing – I tried using Three Good Things in the middle of the night. It wasn’t a perfect solution, but it was a vast improvement over lying helplessly in bed while negative thoughts pummeled me.

The Three Good Things lesson is emblematic of how we encourage teachers in our course – using science, playful cynicism and an open and experimental mindset to apply the evidence-based happiness practices in ways that work for them.

I also encourage students to understand that the strategies I offer are not universally effective. What works for others may not work for them, which is why they should experiment with many different approaches.

What will the course prepare students to do?

The educators leave the course with a written lesson plan they can implement at their school, if they wish. As they deepen their happiness practice, they can also share it with other teachers, their students and their families.

Over the past 16 months, we’ve taught this course to 156 K-12 educators and other school personnel. In a not-yet-published survey that we carried out, more than 30% of the participants scored as clinically depressed prior to starting the class, compared with just under 13% immediately after the class.

This improvement is similar to the results obtained by antidepressant medications and psychotherapy.

The educators also reported overall better health after taking the class. Along with improved sleep, they took fewer sick days, experienced fewer headaches and reported reductions in cold, flu and stomach symptoms.

As resources allow, we plan to tailor these courses to other people with high-stress jobs. Already, we are receiving requests from police officers, health care providers, veterinarians and construction workers.