Exploring the Expanse: 30 Years of Hubble Discoveries
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Exploring the Expanse: 30 Years of Hubble Discoveries



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Exploring the Expanse Hubble Discoveries

Exploring the Expanse: 30 Years of Hubble Discoveries

View the full-size version of the infographic by clicking here.

We’ve been fascinated by space for centuries, but telescopes truly opened our eyes to what lies beyond our frontiers.

For 30 years, the Hubble Space Telescope has been our companion in helping us understand outer space, paving the way for many important scientific discoveries in the process.

A Window to the Universe

Hubble launched on Apr 24, 1990 and has been in our orbit ever since. However, it had something of a shaky start. Due to an error in its primary mirror, it returned many wobbly and blurry images—until a servicing mission in December 1993 fixed the issue.

Today’s incredible map was created by Nadieh Bremer of Visual Cinnamon, for the scientific journal Physics Today. It incorporates over 550,000 scientific observations, to show the diverse objects captured by Hubble between 1990-2019.

Certain constellations have been included to help place these findings, many of which are also visible to the naked eye. Here are the main color-coded categories found on the map:

  • Yellow: Star/ Stellar cluster
    Example: V838 Monocerotis, which includes a red star and a light echo.
  • Red: Galaxy/ Clusters of galaxies
    Example: Spiral galaxy M81, half the size of the Milky Way.
  • Green: Interstellar medium (ISM)
    Example: Eagle Nebula, a majestic spire of cosmic dust and gas, resembling pillars and spanning 4-5 light years.
  • Blue: Solar System
    Example: Jupiter’s Great Red Spot, a high-pressure storm in the planet’s atmosphere.
  • Pink: Calibration/Unidentified (e.g. Hubble Deep Field surveys)
    Example: Ultra Deep Field, which captured a view of 10,000 galaxies over 11 days—some which date back to the early billion years of the universe.

NASA considers the Hubble telescope the “most significant advance in astronomy since Galileo’s telescope” and not without good reason—its total observations top 1.3 million.

Hubble Observations, by Category

The journey doesn’t end there, either. Bremer also looked at the frequency of Hubble observations that occurred within each of these categories, ranging from 1,000-20,000.

Hubble Observation by Category

Source: Physics Today

Each category encompasses multiple distinctive descriptions. For example, galaxies can be broken down further into whether they are spiral, nuclear, elliptical-shaped and much more.

Hubble’s Growing Legacy

The images sent back by Hubble over these three decades are not just for aesthetic purposes. The telescope is also responsible for immense contributions to the astronomy field: close to 13,000 scientific papers have used Hubble as a source to date.

The biggest scientific breakthrough thus far? The realization that our universe is expanding at an accelerating rate—thanks to a force called dark energy.

Hubble really did open up the whole universe to us in a way that nothing else did.

—Colleen Hartman, Former Deputy Center Director, NASA Goddard Space Flight Center

It’s clear that Hubble already has an impressive legacy, and it’s not expected to be retired until at least the year 2025. Soon, it will be joining forces with the new James Webb Space Telescope, to be launched in March 2021. For the next generation of space enthusiasts, their eyes to the skies may well be the Webb instead.

For the true data viz nerds among us, here is an in-depth blog post detailing the sky map’s creation from scratch.

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Animated Map: Visualizing Earth’s Seasons

This map visualizes Earth’s seasons, showing how our planet’s Arctic sea ice and vegetation changes throughout the year.



Animated Map: Visualizing Earth’s Seasons

Why does Earth have seasons?

Many people think the seasons are dictated by Earth’s proximity to the Sun, but this isn’t the case. It’s the Earth’s tilt, not its closeness to the Sun, that influences our seasons.

This animated map by Eleanor Lutz visualizes Earth’s seasons, showing how the temperature changes impact ice levels in the Arctic as well as vegetation more broadly. It also highlights the cloud cover and sunlight each hemisphere receives throughout the year, with each frame in the animation representing a month of time.

Why is Earth Tilted?

Unlike some of the planets that sit completely upright and rotate perpendicularly, Earth rotates on a 23.5-degree axis.

But why? A commonly accepted theory among the scientific community is the giant impact hypothesis. According to this theory, a celestial object called Theia collided with Earth many years ago, when the planet was still forming. This collision not only knocked Earth into its tilted position—some believe that the dust and debris from this impact ended up forming our moon.

Ever since, our planet has been rotating with a slight tilt (which itself is not fixed, as it “wobbles” in cycles), giving us our varying seasons throughout the year.

How Earth’s Tilt Influences our Seasons

As our planet orbits the Sun, it’s always leaning in the same direction. Because of its tilt, the different hemispheres receive varying amounts of sunlight at different times of the year.

In December, Earth is technically closer to the Sun than it is in June or July. However, because the Northern Hemisphere is tilted away from the Sun during December, that part of the planet experiences winter during that time.

Earth's Seasonal Climates

The graphic above by the Smithsonian Science Education Center (SSEC) visualizes Earth’s orbit throughout the year, showing when each hemisphere receives the most direct sunlight (and thus, experiences summer).

The Climate Change Impact

While our seasons have always varied, it’s worth noting that climate change has impacted our seasons, and changed how much Arctic ice we lose each summer.

In the past, millions of miles of ice remained frozen throughout the summer months. In the 1980s, there were 3.8 million square miles of ice in July—that’s roughly the same size as Australia.

Over the years, Arctic ice cover has steadily declined. In July 2020, the ice cover was only 2.8 million square miles—a million less than the amount four decades ago.

Some scientists are predicting that we could lose our summer sea ice entirely by 2035, which would have a devastating impact on the Artic’s wildlife and the indigenous people who live there.

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A Visual Introduction to the Dwarf Planets in our Solar System

Since dwarf planets started being classified in 2005, nine have been recognized. Here we visually introduce the dwarf planets in our solar system.



A Visual Introduction to the Dwarf Planets in our Solar System

Pluto and the Introduction of Dwarf Planets

Since its discovery in 1930, Pluto has been a bit of a puzzle.

For starters, not only is Pluto smaller than any other planet in the solar system, but it’s also smaller than Earth’s moon. It also has an extremely low gravitational pull at only 0.07 times the mass of the objects in its orbit, which is just a fraction of the Moon’s own strength.

At the same time, Pluto’s surface resembles that of terrestrial planets such as Mars, Venus or the Earth, yet its nearest neighbors are the gaseous Jovian planets such as Uranus or Neptune. In fact, Pluto’s orbit is so erratic that it led many scientists to initially believe that it originated elsewhere in space and the Sun’s gravity pulled it in.

These qualities have challenged the scientific view of Pluto’s status as a planet for years. It wasn’t until the discovery of Eris in 2005, one of many increasingly identified trans-Neptunian objects (objects beyond the planet Neptune), that the International Astronomical Union (IAU) defined criteria for classifying planets.

With Eris and other trans-Neptunian objects sharing similar characteristics with Pluto, the definition for dwarf planets was created, and Pluto got downgraded in 2006.

So what are dwarf planets, how do they differ from “true” planets and what are their characteristics?

The History of Dwarf Planets

A dwarf planet is a celestial body that almost meets the definition of a “true” planet. According to the IAU, which sets definitions for planetary science, a planet must:

  1. Orbit the Sun.
  2. Have enough mass to achieve hydrostatic equilibrium and assume a nearly round shape.
  3. Dominate its orbit and not share it with other objects.

Dwarf planets, along with not being moons or satellites, fail to clear the neighborhoods around their orbits. This is the primary reason why Pluto lost its status: because it shares part of its orbit with the Kuiper belt, a dense region of icy space bodies.

Based on this definition, the IAU has recognized five dwarf planets: Pluto, Eris, Makemake, Haumea, and Ceres. There are four more planetary objects*, namely Orcus, Sedna, Gonggong and Quaoar, that the majority of the scientific community recognize as dwarf planets.

Six more could be recognized in the coming years, and as many as 200 or more are hypothesized to exist in the Outer Solar System in the aforementioned Kuiper belt.

Ceres is the earliest known and smallest of the current category of dwarf planets. Previously classified as an asteroid in 1801, it was confirmed to be a dwarf planet in 2006. Ceres lies between Mars and Jupiter in the asteroid belt, and it is the only dwarf planet that orbits closest to Earth.

Here is a brief introduction to the most recognized dwarf planets:

NameRegion of the
Solar System
Orbital period
(in years)
Mean orbital
speed (km/s)
relative to
the Moon
OrcusKuiper belt (plutino)2474.7591026%1
CeresAsteroid belt4.617.994027%0
PlutoKuiper belt (plutino)2484.74237768%5
HaumeaKuiper belt (12:7)2854.531560≈ 45%2
QuaoarKuiper belt (cubewano)2894.51111032%1
MakemakeKuiper belt (cubewano)3064.41143041%1
GonggongScattered disc (10:3)5543.63123035%1
ErisScattered disc5583.62232667%1

Interesting Facts about Dwarf Planets

Here are a few interesting facts about the dwarf planets discovered in our solar system:

Ceres loses 6kg of its mass in steam every second

The Herschel Space Telescope observed plumes of water vapor shooting up from Ceres’ surface; this was the first definitive observation of water vapor in the asteroid belt. This happens when portions of Ceres’ icy surface warm up and turn into steam.

A day on Haumea lasts 3.9 hours

Haumea has a unique appearance due to its rotation, which is so rapid that it compresses the planet into an egg-like shape. Its rotational speed and collisional origin also make Haumea one of the densest dwarf planets discovered to date.

Makemake was named three years after its discovery in 2005

Makemake’s discovery close to Easter influenced both its name and nickname. Before being named after the creator of humanity and god of fertility in the mythos of the Rapa Nui (the native people of Easter Island), Makemake was nicknamed “Easter bunny” by its discoverer Mike Brown.

Eris was once considered for the position of the 10th planet

Eris is the most massive dwarf planet in the solar system, exceeding Pluto’s mass by 28%. As such, it was a serious contender to become the tenth planet but failed to meet the criteria set out by the IAU.

Pluto is one-third ice

The planet’s composition makes up two-thirds rock and one-third ice, mostly a mixture of methane and carbon dioxide. One day on Pluto is 153.6 hours, approximately 6.4 Earth days, making it one of the slowest rotating dwarf planets.

Exploratory Missions and New Planets on the Horizon

With newer technology rapidly available to the scientific community and new exploratory missions getting more data and information about trans-Neptunian objects, our understanding of dwarf planets will increase.

Nestled in the asteroid belt between Mars and Jupiter, the asteroid Hygiea remains a controversy. Hygiea is the fourth largest object in the asteroid belt behind Ceres, Vesta, and Pallas and ticks all the boxes necessary to be classified as a dwarf planet.

So what’s holding back Hygiea’s confirmation as a dwarf planet? The criterion for being massive enough to form a spherical shape is in contention; it remains unclear if its roundness results from collision/impact disruption or its mass/gravity.

Along with Hygiea, other exciting dwarf planets could be soon discovered. Here is a quick rundown of some serious contenders:

Potential Dwarf Planets Under Investigation

120347 Salacia

Discovered in 2004, it is a trans-Neptunian object in the Kuiper belt, approximately 850 kilometers in diameter. As of 2018, it is located about 44.8 astronomical units from the Sun. Salacia’s status is in contention because its planetary density is arguable. It is uncertain if it can exist in hydrostatic equilibrium.

(307261) 2002 MS4

With an estimated diameter of 934±47 kilometers, 2002 MS4 is comparable in size to Ceres. Researchers need more data to determine whether 2002 MS4 is a dwarf planet or not.

(55565) 2002 AW197

Discovered at the Palomar Observatory in 2002, it has a rotation period of 8.8 hours, a moderately red color (similar to Quaoar) and no apparent planetary geology. Its low albedo has made it difficult to determine whether or not it is a dwarf planet.

174567 Varda

Varda takes its name after the queen of the Valar, creator of the stars, one of the most powerful servants of almighty Eru Iluvatar in J. R. R. Tolkien’s fictional mythology. Varda’s status as a dwarf planet is uncertain because its size and albedo suggest it might not be a fully solid body.

(532037) 2013 FY27

This space object has a surface diameter of about 740 kilometers. It orbits the Sun once every 449 years. Researchers need more data on the planet’s mass and density to determine if it is a dwarf planet or not.

(208996) 2003 AZ84

It is approximately 940 kilometers across its longest axis, as it has an elongated shape. This shape is presumably due to its rapid rotation rate of 6.71 hours, similar to that of other dwarf planets like Haumea. Like Varda, it remains unknown if this object has compressed into a fully solid body and thus remains contentious amongst astronomers regarding its planetary status.

*Note: The IAU officially recognizes five dwarf planets. We include four additional dwarf planets widely acknowledged by members of the scientific community, especially amongst leading planetary researchers like Gonzalo Tancredi, Michael Brown, and William Grundy. There are many more potential dwarf planets not listed here that remain under investigation.

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