What is surprising about its size?

It is larger than Jupiter but less massive

Why is it nicknamed Osiris?

Its atmosphere is escaping in a hydrogen tail

What did Spitzer achieve with it in 2005?

Detected infrared light from the planet itself

HD 209458 b Quiz: The First Exoplanet Seen in Transit

A hot gas giant nicknamed Osiris orbits its star every 3.5 days, and this HD 209458 b quiz explains why it became a landmark in exoplanet science. Play an interactive set of 10 questions on the 1999 transit, David Charbonneau, the constellation Pegasus, its inflated radius, Hubble's sodium detection, the evaporating hydrogen tail and Spitzer's first glimpse of exoplanet light.

Start HD 209458 b Quiz

🎯 Daily Trivia Challenge • 🧠 10 Questions • ⏱️ 150 Seconds

Question 1 / 10 Time: 150s

Method
How was HD 209458 b first seen in 1999?
Team
Which astronomer led one of the 1999 transit teams?
Type
What type of planet is HD 209458 b?
Orbit
How long is its orbit?
Constellation
In which constellation is its star?
Radius
What did the transit allow astronomers to measure?
Puffy
What is surprising about its size?
Sodium
Which element did Hubble detect in its atmosphere in 2001?
Tail
Why is it nicknamed Osiris?
Spitzer
What did Spitzer achieve with it in 2005?

Explanations: answer key for all 10 questions

Q1: How was HD 209458 b first seen in 1999?
Answer: As a transit across its star
The star dimmed slightly.
Q2: Which astronomer led one of the 1999 transit teams?
Answer: David Charbonneau
Greg Henry's team also observed it.
Q3: What type of planet is HD 209458 b?
Answer: A hot Jupiter
It orbits very close to its star.
Q4: How long is its orbit?
Answer: About 3.5 days
It whips around its star.
Q5: In which constellation is its star?
Answer: Pegasus
It is about 150 light-years away.
Q6: What did the transit allow astronomers to measure?
Answer: The planet's size
Combined with mass, this gave its density.
Q7: What is surprising about its size?
Answer: It is larger than Jupiter but less massive
Heat inflates it.
Q8: Which element did Hubble detect in its atmosphere in 2001?
Answer: Sodium
It was the first exoplanet atmosphere detected.
Q9: Why is it nicknamed Osiris?
Answer: Its atmosphere is escaping in a hydrogen tail
The star's heat is stripping gas.
Q10: What did Spitzer achieve with it in 2005?
Answer: Detected infrared light from the planet itself
TrES-1 was observed at the same time.

Hd 209458 B Quiz – The First Exoplanet Seen in Transit

HD 209458 b is a hot Jupiter about 150 light-years away in the constellation Pegasus. It orbits its star every 3.5 days, so close that it is heated to over 1,000 degrees Celsius.

In 1999 teams led by David Charbonneau and Greg Henry saw it pass in front of its star, dimming it by about 1.5 percent. It was the first exoplanet seen in transit, which let astronomers measure its radius and show it is puffier than Jupiter but less massive.

In 2001 Hubble detected sodium in its atmosphere, the first exoplanet atmosphere found. Later observations showed hydrogen escaping in a comet-like tail, earning it the nickname Osiris, and in 2005 Spitzer detected its infrared glow.

What This Quiz Teaches

Space fans and students will enjoy these questions.

How it was discovered
What kind of planet it is
What transits reveal
Which atmospheric firsts it holds
Why it has a nickname

Did You Know?

Its star is similar to the Sun.
Transit timing helps find more planets.
Kepler and TESS later found thousands of transiting planets.
Water vapor has been reported in its atmosphere.
It may be tidally locked.