astronomy

Ross 128 b

Ross 128 b 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 Ross 128 b rather than just read about it. In short: Ross 128 b is a confirmed Earth-sized exoplanet, likely rocky, that is orbiting near the inner edge of the habitable zone of the red dwarf star Ross 128, at a distance of 11.007 light-years (3.375 parsecs) from Earth in the constellation of Virgo. The exoplanet was found using a decade's worth of radial velocity data using the European Southern Observatory's HARPS spectrograph (High Accuracy Radial velocity Planet S…

Key takeaways

Ross 128 b belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ross 128 b to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ross 128 b from memory before moving on to harder problems.

Reference excerpt

Ross 128 b is a confirmed Earth-sized exoplanet, likely rocky, that is orbiting near the inner edge of the habitable zone of the red dwarf star Ross 128, at a distance of 11.007 light-years (3.375 parsecs) from Earth in the constellation of Virgo. The exoplanet was found using a decade's worth of radial velocity data using the European Southern Observatory's HARPS spectrograph (High Accuracy Radial velocity Planet Searcher) at the La Silla Observatory in Chile. Ross 128 b is the nearest exoplanet around a quiet red dwarf, and is considered one of the best candidates for habitability. The planet is only 35% more massive than Earth, receives only 38% more starlight, and is expected to be a temperature suitable for liquid water to exist on the surface, if it has an atmosphere. The planet does not transit its host star, which makes atmospheric characterization very difficult.

Physical characteristics

Mass, radius, and temperature Due to it being discovered by the radial velocity method, the only known physical parameter for Ross 128 b is its minimum possible mass. The planet is at least 1.35 M🜨, or 1.35 times the mass of Earth (about 8.06×1024 kg). This is slightly more massive than the similar and nearby Proxima Centauri b, with a minimum mass of 1.27 M🜨. The low mass of Ross 128 b implies that it is most likely a rocky Earth-sized planet with a solid surface. However, its radius, and therefore its density, is not known as no transits of this planet have been observed. Ross 128 b would be 0.5 R🜨 (Earth radii) for a pure-iron composition and 3.0 R🜨 for a pure hydrogen-helium composition, both implausible extremes. For a more plausible Earth-like composition, the planet would need to be about 1.10 R🜨 - i.e., 1.1 times the radius of Earth (approximately 7008 km). With that radius, Ross 128 b would be slightly denser than Earth, due to how a rocky planet would become more compact as it increases in size. It would give the planet a gravitational pull around 10.945 m/s2, or about 1.12 times that of Earth. A 2019 study predicts a true mass about 1.8 times that of Earth and a radius about 1.6 times that of Earth, with large margins of error. Ross 128 b is calculated to have a temperature similar to that of Earth and potentially conducive to the development of life. The discovery team modelled the planet's potential equilibrium temperature using albedos of 0.100, 0.367, and 0.750. Albedo is the portion of the light that is reflected instead of absorbed by a celestial object. With these three albedo parameters, Ross 128 b would have a Teq of either 294 K (21 °C; 70 °F), 269 K (−4 °C; 25 °F), or 213 K (−60 °C; −76 °F). For an Earth-like albedo of 0.3, the planet would have an equilibrium temperature of 280 K (7 °C; 44 °F), about 8 Kelvins lower than Earth's average temperature. The actual temperature of Ross 128 b depends on yet-unknown atmospheric parameters, if it has an atmosphere.

Host star

Ross 128 b orbits the small red dwarf star known as Ross 128. The star is 17% the mass and 20% the radius of that of the Sun. It has a temperature of 3192 K, a luminosity of 0.00362 L☉, and an age of 9.45±0.60 billion years. For comparison, the Sun has a temperature of 5772 K and age of 4.5 billion years, making Ross 128 half the temperature and over twice the age. The star is only 11.03 light-years away, making it one of the 20 closest stars known. In 2018, astronomers, based on near-infrared, high-resolution spectra (APOGEE Spectra), determined the chemical abundances of several elements (C, O, Mg, Al, K, Ca, Ti, and Fe) present in Ross 128, finding that the star has near solar metallicity.

Orbit Ross 128 b is a closely orbiting planet, with a year (orbital period) lasting about 9.9 days. Its semi-major axis is 0.0496 AU (7.42 million km). According to some models of the planet's orbit, its orbit is quite circular, with an eccentricity of around 0.03, but also with a large error range as well. However, if all the orbital models are brought together then the eccentricity is higher at about 0.116, and again this is subject to a large error range. Compared to the Earth's average distance from the Sun of 149 million km, Ross 128 b orbits 20 times closer. At that close distance from its host star, the planet is most likely tidally locked, meaning that one side of the planet would have eternal daylight and the other would be in darkness. A 2024 study of the radial velocity data found an eccentricity of about 0.21 for Ross 128 b, higher than previous estimates and similar to that of Mercury. Given the planet's orbit near the inner edge of the habitable zone, such a high eccentricity would significantly decrease its potential for habitability.

Habitability

Stellar flux properties Ross 128 b is not confirmed to be orbiting exactly within the habitable zone. It appears to reside within the inner edge, as it receives approximately 38% more sunlight than Earth. The habitable zone is defined as the region around a star where temperatures are just right for a planet with a thick enough atmosphere to support liquid water, a key ingredient in the development of life as we know it. With its moderately high stellar flux, Ross 128 b is likely more prone to water loss, mainly on the side directly facing the star. However, an Earth-like atmosphere, assuming one exists, would be able to distribute the energy received from the star around the planet and allow more areas to potentially hold liquid water. In addition, study author Xavier Bonfils noted the possibility of significant cloud cover on the star-facing side, which would block out much incoming stellar energy and help keep the planet cool.

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Illustrations

Worked examples

Example 1 — a first encounter with Ross 128 b

Start with the simplest possible case. Write down what Ross 128 b 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 Ross 128 b 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 Ross 128 b 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 Ross 128 b

In research: Ross 128 b 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 Ross 128 b 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: Ross 128 b is common in secondary-school and first-year university syllabi. It links to neighbouring topics Exoplanets detected by radial velocity, Exoplanets discovered in 2017, Near-Earth-sized exoplanets, so understanding it makes those chapters shorter.
In everyday life: Look for Ross 128 b 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 Ross 128 b in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ross 128 b 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 Ross 128 b out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ross 128 b in simple terms?

Why does Ross 128 b 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 Ross 128 b?

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 Ross 128 b.