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Open Access
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A&A
Volume 689, September 2024
Article Number A334
Number of page(s) 12
Section Catalogs and data
DOI https://doi.org/10.1051/0004-6361/202450495
Published online 23 September 2024

© The Authors 2024

Licence Creative CommonsOpen Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.

1 Introduction

The planetary defense concept relates directly to natural hazards posed by asteroids and comets (Chapman 1994). The concept defines the capabilities needed to detect and warn of potential asteroid or comet impacts with Earth. The concept also assess the possibility of preventing or mitigating the effect of such an event. The activities related to this concept consist of finding and tracking near-Earth objects (NEOs) with a non-zero probability of impacting Earth; the characterization of objects to determine their orbit trajectory, size, shape, mass, composition, rotational dynamics, and other parameters; and planning (and implementing) a set of measures to deflect or disrupt an object that would impact Earth (Harris et al. 2013).

Notably, DART (together with the LICIA cube) is the first space mission labeled as a “planetary defense” mission, and it has produced technological and scientific results related to a mitigation process for the binary asteroid Didymos-Dymorphos (Thomas et al. 2023; Graykowski et al. 2023; Terik Daly et al. 2023; Jian-Yang et al. 2023; Dotto et al. 2024). All of these achievements were possible through the technological maturity of the kinetic impactor and the scientific knowledge of the asteroid’s properties.

The population of NEOs is increasing constantly due to newly discovered objects, and the characterization of physical parameters (mass, shape, mineralogy, internal structure) should follow the trend of discoveries. Through the perspective of the planetary defense concept, characterizing the parameters of potentially hazardous asteroids (PHAs) is of the highest importance1.

One of the objectives of NEOROCKS is to characterize as many PHAs as possible in terms of their colors (Hromakina et al. 2021, 2023). NEOs have small diameters and can be observed from ground-based telescopes during close encounters with Earth. Their favorable geometries, sometimes for a time period of hours and days, need to be used to perform as many observations as possible in order to have access to several parameters that will ultimately aid in constraining their mass, shape, surface composition, surface rugosity, and internal structure (Birlan et al. 2015).

Colors, together with spectra, and possible records from polarimetric and radar data are essential for the characterization of NEOs. Images of the shapes of NEOs visited by spacecrafts allow for derivation of a rubble pile structure (Fujiwara et al. 2006; Arakawa et al. 2020; DellaGiustina et al. 2019). This rubble pile structure is scalable even to large main belt asteroids, through the use of adaptive optics observations and photometric measurements (Vernazza et al. 2021, 2020).

This paper presents the final results of a color survey conducted within the framework of the NEOROCKS project, which aims to characterize PHAs and small NEOs by obtaining their surface colors and classifying them into taxonomic classes. The paper is organized as follows: in Section 2, we describe the observations and main results. In Section 3, we present the taxonomic classification of the observed NEOs. The final results of the NEOROCKS database and our analysis and discussion are presented in Section 4. The conclusions of this work are presented in Section 5. Tables and individual graphs of newly observed objects are presented in the appendix. This paper presents the newly observed asteroids, while the statistical analysis was made on the whole color database realized in the frame of the NEOROCKS program (Hromakina et al. 2021, 2023).

2 Observations and results

The NEOROCKS color survey was conducted between 2020 and 2023. Initially scheduled to take place between 2020 and 2022, the program was extended to a third year because of the situation caused by COVID-19 pandemic.

The choice of asteroid targets for each run of the NEOROCKS color survey was opportunistic. Scheduled as top priorities were the PHAs visible during the run. This was followed by objects observed in a coordinated manner inside the consortium. Priority was also given to observations of NEOs with unknown colors. Finally, newly discovered objects were also scheduled in order to take advantage of their favorable window of observations.

Among our dataset of newly observed objects, 34% of them are classified as PHAs, 56% are Apollo-type objects, and 7% are classified as Athen. Table A.1 contains the results of the taxonomic classification described in Section 3.

For the survey, observational time for two 1m class assets was scheduled in France at the 1.2 m telescope at the Observatoire de Haute Provence and the 1.05 m telescope of the Pic du Midi Observatory. Our strategy was to allot 50% of the observational time to each telescope. Further, in 2021, our strategy changed when the telescope at the Pic du Midi started the process of reconditioning. Thus, the largest part of our survey and data were obtained with the telescope at the Observatoire de Haute Provence.

For the observations recorded at the Observatoire de Haute Provence, the 1.2 m telescope was equipped with a 2048 × 2048 Andor Ikon L 936 CCD camera that has a field of view of 13.10′ × 13.10′ (Hromakina et al. 2021). The 2×2 binning resulted in a pixel scale of 0.7700″/px, and the broadband filters BV (Johnson system) and RI (Cousins) were used. The 1m telescope at the Pic du Midi was equipped with an iKon-L Andor CCD camera with a 2k × 2k E2V detector (field of view 14.8′ × 14.8′, binning 2×2) and the Sloan griz filters were used (Dumitru et al. 2018b). The observations were recorded with an average seeing of 2.5″ at the Pic du Midi and 3.7″ at the Observatoire de Haute Provence.

Each object was observed for about an hour. Depending on the exposure time, from 30 seconds to three minutes, the recorded images were in the three to 15 in each filter. The images in each filter were taken sequentially in order to minimize any possible magnitude variation due to the rotation (spin) of the object. The significant extinction of the targets in the B filter limit our survey to objects with a V magnitude lower than 19 mag.

Data reduction was done with a standard procedure described in Hromakina et al. (2021). The instrumental magnitudes were measured for the target and field stars using aperture photometry. Then, absolute calibration was done using magnitudes of field stars in the Pan-STARRS catalog. To transform the star magnitudes from the Sloan photometric system of the Pan-STARRS1 catalog into the Johnson-Cousins system, the transforming equations presented in Kostov & Bonev (2018) were used.

Colors of 83 newly observed asteroids are presented in Table A.1, which contains the photometry, estimated absolute magnitudes, and observational circumstances. Some of them were observed during two or more nights. This paper presents individual colors of each night instead of an average value (we refer here to the procedure described in Hromakina et al. (2023) for the computation of absolute magnitude). Some values of colors (mainly the B-V) are not available in Table A.1 for two reasons: either the S/N ratio is low, and thus less important for reliable results, or the sky condition and the apparent magnitude of the object were not adapted to compute the B magnitude.

3 Classification in Bus-DeMeo taxonomy

Taxonomic classification was done using the obtained surface colors B-V, V-R, and V-I, which were transformed into reflectances using the following equation: R(λ)=10−0.4[(Mλ−MV)−(Mλ−MV)⊙],$\[R(\lambda)=10^{-0.4\left[\left(M_\lambda-M_V\right)-\left(M_\lambda-M_V\right)_{\odot}\right]},\]$(1)

where (Mλ − MV) and (Mλ − MV)⊙ are the colors of the object and the Sun at the wavelength λ, respectively. Solar colors were taken from Holmberg et al. (2006). The obtained reflectance was normalized at the central wavelength of the V-filter. Then, using the M4AST service (Popescu et al. 2012; Birlan et al. 2016), the resulting spectra were compared to the mean spectra of the taxonomic classes in Bus-DeMeo classification (DeMeo et al. 2009). As our taxonomic classification is based on only three or four data points2, it is not nearly as precise as spectral data. The papers consider only major Bus-DeMeo taxonomic classes, namely S-complex (Q-type asteroids are included in the S-complex), C-complex, X-complex, A-type, D-type, and V-type.

The estimated taxonomic classes are shown in Table A.1. If there was an unambiguous match to a specific sub-type, we indicate it before the complex it falls in. Individual colors of the newly observed objects together with the mean spectra of the best-matching taxonomic class are presented at the EU Open Research Repository (https://zenodo.org/records/13164513). Two objects of our sample, namely (143649) 2003 QQ47 and (185853) 2000 ER70, were not classified because of a lack of colors (either the objects are too faint to be observed in several bands or the differential movement is too significant to reach a good S/N ratio).

We checked our classification using color–color plots (Figure 1). Only asteroids with unambiguous taxonomic classification are presented in the figure.

The taxonomic classification process of the newly observed objects had following percentages: 39% of objects are classified as S-type objects, 21% are classified as X-types 15% are C-type, 9% are D-type, and 2% are A-type asteroids. For 8% of the sample, a double affinity to a taxonomic class was found, while the rest of the asteroids were not classified until the completion of our sample (two objects).

Figure 1 shows the distinction between the C and S class on B-V and V-R colors. The C-taxon in our sample has an average V-R and B-V color lower than the one of the S-taxon. The X-taxon has an intermediate value clearly located between these two large classes. Asteroids belonging to D-taxon are located at the top of both color–color graphs, which are interpreted in terms of the increase of the values of R and I colors compared to other taxonomic classes (i.e., the computed slope of the measured values is greater than that of other classes).

Interestingly, two asteroids from the sample, namely (226554) 2003 WR21 and (482250) 2011 LL2, show an affinity to the small A-taxon. Both asteroids were discovered by the Catalina Sky Survey. Both asteroids are PHAs; 226554 is an Apollo-type asteroid, while 482250 is an Amor type. The lack of data in the literature for these two asteroids does not allow for in-depth analysis. Indeed, the cross-check on the Small Bodies Node asteroid, comet, and satellite datasets (Ferret3 and the compiled MP3C database (Delbo et al. 2022)) for the asteroid 226554 shows just a NEOWISE albedo of 0.125 (Mainzer et al. 2014), which is half the average IRAS thermal albedo of A-class (Fulchignoni et al. 2000). In the updated NEOWISE albedo database (Masiero et al. 2020), the thermal albedo of 226554 is 0.434±0.341. This value covers many other taxonomic classes due to its large excursion of errors. The searches for colors or spectral values for 482250 gave negative results4.

The relevance of the taxonomical association of asteroids in our sample has been tested using one of the largest databases of NEOs published by the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) (Binzel et al. 2019). MITHNEOS covered the reflectance spectra in the visible and near-infrared (up to 2.5 μm) for more than 1,400 NEOs. From our sample of 81 objects, only 17% of the classified asteroids have also been found in the MITHNEOS database. This is an important result that brings forth the importance of NEOROCKS’s survey of colors.

While NEOROCKS is poor in data, with only four colors being observed, a key aspect to evaluate is how good of a match the taxonomic association of the asteroids has with the one obtained using spectral data of MITHNEOS. Indeed, the taxonomy obtained via the NEOROCKS survey is globally in good agreement with the one of MITHNEOS, if we consider the representative and large classes. However, we must note that two of the objects studied here, namely (215188) 2000 NM and (297418) 2000 SP43, have an affinity for the S-complex, but they are classified as V-type by MITHNEOS. This difference is reasonable because these taxonomic classes have a similar spectra in the visible region, and they are clearly distinguishable in the near-infrared region of the spectrum; notably, the V-type shows large absorption bands around 1 and 2 μm. The thermal albedo of the asteroid 297418 was compiled by Masiero et al. (2020), and it is 0.377−0.202+0.130$\[0.377_{-0.202}^{+0.130}\]$. This value could not avoid S-type nor V-type classification.

The asteroid (98943) 2001 CC21, a future target of the extended Hayabusha2 mission, was observed during the survey (Geem et al. 2023; Yamada et al. 2023). The colors obtained in the NEOROCKS survey were also superimposed with spectral data from the literature (Lazzarin et al. 2005). Our data are in agreement with the spectroscopic one; that is, this object was identified as belonging to the S-complex. A detailed study including spectroscopic, photometric, color, and light curve analyses as well as thermal modeling of this asteroid has now been published (Fornasier et al. 2024).

thumbnail Fig. 1

Color–color diagrams showing main taxonomic classes for our dataset, together with the error bars. Silicate-type objects are in green, carbonaceous-like objects are in red, the X-complex is in blue, and D-type objects are in black.

4 NEOROCKS photometric survey and final results

Between 2020 and 2023, the NEOROCKS color survey observed, computed, and recorded 170 NEOs. Of this sample, 38% (i.e., 61 objects) have been classified as PHAs. This result is in line with and fulfills the requirements of the NEOROCKS program.

The largest part of the survey involved French facilities, namely the Observatoire de Haute Provence 1.2m telescope and partly the Pic du Midi 1m telescope, for a total of 64 nights. During the survey, partial results were published (Hromakina et al. 2023, 2021). Rotational periods were also computed and reported as byproducts of this survey (Birlan et al. 2022).

The experiment, called the Rapid Reaction Experiment, was done during the NEOROCKS project (Perozzi et al. 2023). This experiment consisted of coordinated observations of one or several specific targets, and it was conducted in order to synchronize the activities and the reaction of members of the consortium using all the available assets. Our team contribution was, obviously, toward color index observations.

Several objects were also observed two or more times during the consecutive nights on the same run, or in different runs (i.e., different geometries of observations) during the survey. Their datasets allowed us to assess the robust affinity of these objects to a taxon or a complex of taxons.

The average colors of taxons S, C, X, and D were computed as in Hromakina et al. (2023) and compared with the similar ones from the literature (DeMeo et al. 2009; Ieva et al. 2018; Lin et al. 2018). These values are presented in Table 1. The average colors obtained for the NEOROCKS survey of colors are in good agreement with the literature, within the standard errors.

Statistics of the number of objects versus their estimated diameters is presented in Fig. 2. As expected, the NEOROCKS database of colors contains, in a large majority (64%), objects with diameters smaller than 1 km.

The photometric survey of colors contains 159 objects that have one established taxon. Eleven objects (approximately 7% of our database) have an ambiguous association (two, three, or no taxons).

The statistics of the 159 objects show that a large fraction of NEOs exhibit an affinity to the S-taxonomic complex (43%). The C-complex taxons represent 16% of our database, D-type represents 13%, and X-complex represents 23%. The end-members A- and V-type represent 3% and 2%, respectively. Taxonomy and estimated diameter of each asteroid are presented in Table A.3.

Figure 2 reveals that for objects with diameters smaller than 500 m, the sample is largely dominated by asteroids belonging to S-complex (60%), while C-complex seems to be underrepresented (23%). This result is in line with the one presented by Binzel et al. (2019), using their MITHNEOS spectral data (see Fig. 7 in their article). However, these ratios are subject to biases. Overall, the surveys record bright objects more easily (i.e., objects that exhibit high albedos). Marsset et al. (2022) presented a debiased compositional distribution of NEOs using the statistical approach of debiasing proposed by Granvik et al. (2018). In their sample consisting of MITHNEOS data plus another 420 NEAs, the bias-corrected population contains 42% of asteroids from the S-complex and 40% of asteroids from C-complex (Marsset et al. 2022).

The NEOROCKS color survey is based on records for the broadbands B, V, R, and I. The taxonomic classification of the observed asteroids is seen as an affinity of these objects to a specific taxon or a complex of taxons. The product of this survey is synthesized in three colors or less; thus, the plot of asteroids in a 3D space of colors could give a perception of our sample. Figure 3 presents the representative distribution of taxonomic complex of taxons for our database. For this plot only, the reliable asteroids with three colors were taken into consideration. When one object was observed several times and there was no ambiguity between the datasets on the taxons for the object, then an average for colors was considered.

From Fig. 3, it is quite easy to distinguish between taxonomic classes. Thus, for the end-member D and A taxonomic classes, the relevance of the V-I color is obvious. The V-R color is quite representative for distinguishing between the C- and S-complex. The X-complex is relatively well seen as a cluster between C and S taxonomic complexes.

There are quite a few asteroids in our sample that have been investigated by complementary methods (spectroscopy, radiometry, radar, polarimetry). Through this perspective, the data obtained during the NEOROCKS color survey are very important and could be seen as a starting point for future investigations regarding the physics and mineralogy of recorded asteroids.

We investigated the possibility that an object from the NEOROCKS color database could be associated with a meteor shower as a parent body. For this we used the approach from Dumitru et al. (2017), which is based on three metrics in the space of orbital elements (Dumitru et al. 2018a). The computation was made using the newest orbital elements of all NEOs and the latest data of meteor showers5. The metrics used in the association of asteroids with meteor showers were proposed by Southworth and Hawkins (Southworth & Hawkins 1963), Jopek (Jopek 1993), and Asher (Asher et al. 1993). The results are presented in Table 2.

From our sample, only one asteroid was associated by two metrics with a meteor shower, namely 2011 OL51. This object is characterized by a Tisserand parameter with Jupiter TJ=2.858, a high eccentricity of its orbits (e=0.639), and an aphelion distance Q=5.102 au, which fulfills the condition of objects highly influenced by the gravitational field of the planet Jupiter. This object has an unstable orbit (Lyapunov time of 50 yr, as computed in Table A.2) and might be an inactive comet (Fernández et al. 2014). Thus, the contribution of this object to the flux of meteoroids supplying the OCC meteor shower is plausible.

An investigation of orbit stability was done by numerical integration, calculating the Lyapunov times (TL) by numerical integrating the equations of motion alongside the variational equations in order to estimate the maximum Lyapunov exponent. The log of the norm of the variational vector was recorded every 100 years, and these values were used to fit a maximum Lyapunov exponent (Morbidelli & Nesvorný 1999; Tancredi et al. 2001).

For each asteroid, the nominal orbit was integrated forward in time, for 10000 years, which is approximately 50 times the typical value of the TL for NEOs. The dynamical model of the Solar System includes all the planets as well as Pluto, Ceres, Pallas, and Vesta as perturbing bodies. The Earth and the Moon were treated as separate bodies. The model accounts for the Sun’s relative contribution and uses the modified Bulirsch–Stoer algorithm adapted to an 80-bit extended precision data type (Nedelcu et al. 2014; Dumitru et al. 2018b).

The results are presented in Table A.2. As presented in Fig. 4, the average of TL for the NEOROCKS color database is around 100 years.

The wing with small TL (i.e., large chaoticity) contains the asteroid (99942) Apophis. This asteroid will have a close encounter with Earth on April 13, 2029. The European Space Agency has at least two concepts of mission for in situ investigation of this asteroid: SATIS6 and RAMSES (Kueppers et al. 2023; Morelli et al. 2024), while NASA has decided to investigate Apophis using the new OSIRIS-APEX concept of mission (DellaGiustina et al. 2023). A second object located in a highly chaotic region (TL = 17 years) is 2022 RB5. This object has multiple close approaches with the Earth in the next 100 years. Both objects have small MOIDs (0.00007 and 0.00829 au).

At the other wing of the statistical distribution (Figure 4), we have the asteroid (143649) 2003 QQ47, with a TL = 3384 years and a MOID of 0.00289. This anticorrelation between MOID and TL is due to a high inclination of its orbit (i=62°), which protects it from longer close approaches with Earth.

Another peculiar case is the asteroid (317643) 2003 FH1, which has a TL of 50 years and a MOID of 0.20345 au. According to NEODYS7, (Bernardi et al. 2021) this object has multiple close approaches with Venus (at 0.01 au) and Mars (at 0.036 a.u).

Close approaches of NEOs with Earth are also a major concern and are the subject of investigation for our survey. Indeed, the prevention of a possible a catastrophic collision with our planet is an important aspect, and a collision can be mitigated by good knowledge of the size, shape, mineralogical composition, and internal structure of the impactor.

For this, we computed the MOID for all objects of our sample (Table A.2), and we corroborated them with the taxonomy of the objects and the amount of ΔV corresponding to a spacecraft that will conduct an in situ investigation of the asteroid. The results are presented in Fig. 5. In this figure, the dashed line delimits the region (lower left) in which MOID is lower than 0.05 au and ΔV is smaller than 7 km/s. Table 3 presents all asteroids that fall into this region, together with the associated class and the uncertainty of their orbits. Among these objects, 45% are S-types, 16% are C-types, and 22% are X-types. Asteroids (226554) 2003 WR21 and 2017 SE19 present characteristics similar to the A taxon, while (177614) 2004 HK33 and 2022 VV2 are more akin to D-type ones. Asteroid (163014) 2001 UA5 was classified as a D-type by Hromakina et al. (2021). This asteroid was also observed in spectroscopy by Binzel et al. (2004), who classified it as an Sq type. The paucity of our data (only four points), as well as the lower value of B reflectance in our database of colors for this object could be subject of a misclassified taxon.

One column of Table 3 contains the estimated diameters for the low-ΔV objects. For this, we used the values computed by Mainzer et al. (2019). These data are available for a small amount of asteroids from Table 3. The rest of the values for diameters were computed using the absolute magnitude of the object together with the average albedo of the taxon from Fulchignoni et al. (2000) and using the individual classification of each of them.

The excess of S-type asteroids among small-sized objects (Fig. 2) is definitely related to a bias of our sample – it is most probably highly correlated with the reflectivity properties of surfaces. Indeed, the results published by Marsset et al. (2022) regarding the ratio of S-type versus C-type asteroids in the NEO population have now been confirmed by new results regarding the origin of these two taxons. The A-complex analysis of source regions of carbonaceous meteoroids, meteorites, and the NEO population (Brož et al. 2024) has revealed that the flux of meter-sized extraterrestrial material that interacts with Earth should be composed of S- and C-type objects in an approximately equal quantity. These findings are consistent with the results of Nesvorný et al. (2023), who inferred that the contribution of inactive comets to the NEO population is smaller than previously estimated (1.7% compared to 6% calculated by Bottke et al. 2022).

Table 1

Average colors obtained for NEOROCKS photometric survey of colors and the comparison with the values from DeMeo et al. (2009), Ieva et al. (2018), and Lin et al. (2018).

thumbnail Fig. 2

Size distribution of the entire dataset of the NEOROCKS color survey.
thumbnail Fig. 3

Distribution of the taxonomic classes obtained for all objects of the NEOROCKS survey color data.
Table 2

Asteroids from the NEOROCKS color database associated with meteor showers.

thumbnail Fig. 4

Statistics of the Lyapunov Time (TL) for the for the NEAs observed in the NEOROCKS color survey.
thumbnail Fig. 5

Earth’s MOID versus the ΔV value for the NEOs in our dataset. Vertical and horizontal dashed lines at MOID = 0.05 au and ΔV = 7 km/s, respectively, separate objects that may be suitable as space mission targets. One zoom into the region 0–0.1 au of MOID and 0–10 km/s in ΔV allowed us to distinguish between the color codes taxons for asteroids.
Table 3

NEOs that could be potential space mission targets based on their low MOID and low ΔV.

5 Summary and conclusions

We have presented new observational data for 83 small NEOs obtained within the NEOROCKS project. For these asteroids, we computed their surface colors and estimated their class, absolute magnitude, and diameter.

The final results of the NEOROCKS color database are composed of 170 objects that were observed for more than 63 nights between 2020 and 2023. Most of these observations were carried out at the Observatoire de Haute Provence in France. A few observations were performed at the Pic du Midi Observatory (also in France). The survey was done in four broadband filters, namely B, V, R, and I. The sample also contains values of colors for asteroid (99942) Apophis, which will graze the Earth on April 13, 2029.

The taxonomical classification of the asteroids contained in the sample of the NEOROCKS color database allows one to distinguish between the major taxons. For a few objects, however, the classification allows one to identify the affinity for end members, such as the A, D, and V taxons. The V-I color allowed us to distinguish D and A-type objects while, the V-R color allowed us to distinguish more between S- and C-taxons.

The statistics of the taxonomical types clearly indicate a large percentage of rocky silicate-rich asteroids (S-complex taxon). For objects with diameters smaller than 500 m, approximately 59% of them are S-type objects. This large percentage is mainly due to a bias induced by the surface reflectivity of objects (S-type asteroids are more reflective than C-type objects).

The chaos for the objects of the NEOROCKS color database was determined using the Lyapunov time of each object. The statistics show that the average Lyapunov time does not go beyond 100 years.

Several objects of the NEOROCKS color database have orbits similar to those of meteoroids associated with meteor showers. Among them, the asteroid 2011 OL51 was validated by two metrics used for this investigation, and it may be one of the parent bodies of the OCC meteor shower.

Thirty-one NEOs in our sample have ΔV<7 km/s, indicating that these objects might be reachable targets for a future space mission. Among these objects, there are two D-type objects (2004 HK33 and 2022 VV) and two A-type objects (2003 WR21 and 2017 SE19).

Acknowledgements

We acknowledge funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 870403. The article is based in part on observations made at Observatoire de Haute Provence (CNRS), France. IB thanks the French PAUSE program, which provides support to scientists at risk.

Appendix A Results of newly observed objects

Table A.1

Observational circumstances and results.

Table A.2

Observed objects, Lyapunov time, and MOIDs for the NEOROCKS color database. The list is organized in order of increasing Lyapunov time.

Table A.3

Asteroid taxonomy and diameter.

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1

These are asteroids with a minimum orbital intersection distance (MOID) of less than 0.05 au and an absolute magnitude H<22.

2

Spectral reflectance values have been normalized to the visible; thus, the V value has no statistical meaning.

4

Asteroid 482250 is a fast rotator (Hergenrother et al. 2012).

All Tables

Table 1

Average colors obtained for NEOROCKS photometric survey of colors and the comparison with the values from DeMeo et al. (2009), Ieva et al. (2018), and Lin et al. (2018).

In the text
Table 2

Asteroids from the NEOROCKS color database associated with meteor showers.

In the text
Table 3

NEOs that could be potential space mission targets based on their low MOID and low ΔV.

In the text
Table A.1

Observational circumstances and results.

In the text
Table A.2

Observed objects, Lyapunov time, and MOIDs for the NEOROCKS color database. The list is organized in order of increasing Lyapunov time.

In the text
Table A.3

Asteroid taxonomy and diameter.

In the text

All Figures

thumbnail Fig. 1

Color–color diagrams showing main taxonomic classes for our dataset, together with the error bars. Silicate-type objects are in green, carbonaceous-like objects are in red, the X-complex is in blue, and D-type objects are in black.
In the text
thumbnail Fig. 2

Size distribution of the entire dataset of the NEOROCKS color survey.
In the text
thumbnail Fig. 3

Distribution of the taxonomic classes obtained for all objects of the NEOROCKS survey color data.
In the text
thumbnail Fig. 4

Statistics of the Lyapunov Time (TL) for the for the NEAs observed in the NEOROCKS color survey.
In the text
thumbnail Fig. 5

Earth’s MOID versus the ΔV value for the NEOs in our dataset. Vertical and horizontal dashed lines at MOID = 0.05 au and ΔV = 7 km/s, respectively, separate objects that may be suitable as space mission targets. One zoom into the region 0–0.1 au of MOID and 0–10 km/s in ΔV allowed us to distinguish between the color codes taxons for asteroids.
In the text

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