astronomy

GJ 3929

GJ 3929 is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand GJ 3929 rather than just read about it. In short: GJ 3929, also known as Gliese 3929 and TOI-2013, is a red dwarf star located 51.6 light-years (18.6 parsecs) from Earth, in the constellation Corona Borealis. With an apparent magnitude of 12, it is not visible to the naked eye.

Key takeaways

GJ 3929 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GJ 3929 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GJ 3929 from memory before moving on to harder problems.

Reference excerpt

GJ 3929, also known as Gliese 3929 and TOI-2013, is a red dwarf star located 51.6 light-years (18.6 parsecs) from Earth, in the constellation Corona Borealis. With an apparent magnitude of 12, it is not visible to the naked eye. In 2022, two exoplanets were detected orbiting the star.

Characteristics GJ 3929 is a red dwarf of spectral type M3.5V, having a radius of 0.32±0.01 R☉, a mass of 0.313+0.027−0.022 M☉ and a temperature of 3384±88 K. With an apparent magnitude of 12.7, it cannot be seen with the naked eye or with a small telescope. It has no companion stars and its age is estimated at 7.1 billion years, give or take four or five billion. The star is located in the northern hemisphere, approximately 50 light years from Earth, in the direction of the constellation Corona Borealis. Its closest neighbor is the red dwarf G 179–57, located at a distance of 3.9 light years.

Planetary system

In 2022, two exoplanets were detected orbiting around GJ 3929. The innermost, GJ 3929 b, is a rocky planet just 9% larger than Earth, while the outermost, GJ 3929 c, is a sub-Neptune with 5.7 times the mass of Earth. An additional planet candidate was discovered from follow-up radial velocity analysis in 2025 The three planets orbit inside (ie. hotter than) the star's habitable zone.

GJ 3929 b

The innermost planet, GJ 3929 b (TOI-2013 b), is an Earth-sized planet discovered by the transit method. Orbiting its star at a distance of 0.0252 astronomical units (3,770,000 km), the planet is located in its star's Venus zone, and completes a revolution every 2 days and 15 hours. The planet's equilibrium temperature is calculated at 568 K (295 °C), and it receives a planetary insolation 17 times greater than what the Earth receives from the Sun. The planet's mass is calculated at 1.75±0.45 M🜨 according to photometric observations using the NEID spectrometer. Observations using the ARCTIC imager, plus photometry from TESS and LCOGT, constrained the planet's radius to 1.09±0.04 R🜨. This radius makes GJ 3929 b very similar to Earth in terms of size. It was discovered by a team of astronomers led by Jonas Kemmer. They reported a planetary transit signal in the host star's light curve. Subsequent observations, mainly with the CARMENES spectrograph, revealed that this transit signal is an orbiting exoplanet. Due to the apparent brightness of the host star and its small size, GJ 3929 b is an excellent planet for atmospheric study with the James Webb Space Telescope. Observations have found no detected molecular features, which rules out certain compositions such as a thick atmosphere rich in carbon dioxide. The observations also measured the dayside temperature, which is consistent with that of a zero-albedo planet with no heat distribution, and indicate that GJ 3929 b is likely bare rock.

GJ 3929 c The outermost planet, GJ 3929 c (TOI-2013 c) is a sub-Neptune discovered using the Radial velocity method. It orbits its star at a distance of 0.081 astronomical units (12,100,000 km), 3 times further away than GJ 3929 b, but still below GJ 3929's habitable zone, completing an orbit every 15 days. Its minimum mass is 5.71±0.94 M🜨, while its radius is unknown. Estimates using mass-radius relationship derive a radius of 2.26 R🜨. Its equilibrium temperature is calculated at 317 K (44 °C), and it receives a planetary insolation 68% greater than what the Earth receives from the Sun. GJ 3929 c was first identified in radial velocity data, which indicated the existence of another planet besides GJ 3929 b. Initially, it was just an exoplanet candidate, but it was later confirmed by a team led by Corey Beard. Because its orbital period (15 days) is far from its star's rotation period (122 days), it is unlikely that the radial velocity signal is actually an artifact of its parent star's activity and rotation.

Worked examples

Example 1 — a first encounter with GJ 3929

Start with the simplest possible case. Write down what GJ 3929 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to GJ 3929 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about GJ 3929 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of GJ 3929

In research: GJ 3929 appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses GJ 3929 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: GJ 3929 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Corona Borealis, Gliese and GJ objects, M-type main-sequence stars, so understanding it makes those chapters shorter.
In everyday life: Look for GJ 3929 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study GJ 3929 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GJ 3929 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain GJ 3929 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GJ 3929 in simple terms?

Why does GJ 3929 matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study GJ 3929?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on GJ 3929.